Switch docs to MKDocs (#602)

Fixes #601. Merged in 6f87b32 from the md3 branch and did a lot of cleanup.

Changes include:

* Removed old docs build tool, templates, etc.

* Added MkDocs config file, etc.

* filename.txt => filename.md

* pythonhost.org/Markdown => Python-Markdown.github.io

* Markdown lint and other cleanup.

* Automate pages deployment in makefile with `mkdocs gh-deploy`

    Assumes a git remote is set up named "pages". Do

        git remote add pages https://github.com/Python-Markdown/Python-Markdown.github.io.git

    ... before running `make deploy` the first time.

1 files changed, 306 insertions, 0 deletions

diff --git a/docs/change_log/release-2.6.md b/docs/change_log/release-2.6.md
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+title: Release Notes for v2.6
+
+# Python-Markdown 2.6 Release Notes
+
+We are pleased to release Python-Markdown 2.6 which adds a few new features
+and fixes various bugs. See the list of changes below for details.
+
+Python-Markdown version 2.6 supports Python versions 2.7, 3.2, 3.3, and 3.4 as
+well as PyPy.
+
+## Backwards-incompatible Changes
+
+### `safe_mode` Deprecated
+
+Both `safe_mode` and the associated `html_replacement_text` keywords are
+deprecated in version 2.6 and will raise a **`DeprecationWarning`**. The
+`safe_mode` and `html_replacement_text` keywords will be ignored in the next
+release. The so-called "safe mode" was never actually "safe" which has resulted
+in many people having a false sense of security when using it. As an
+alternative, the developers of Python-Markdown recommend that any untrusted
+content be passed through an HTML sanitizer (like [Bleach]) after being
+converted to HTML by markdown. In fact, [Bleach Whitelist] provides a curated
+list of tags, attributes, and styles suitable for filtering user-provided HTML
+using bleach.
+
+If your code previously looked like this:
+
+```python
+html = markdown.markdown(text, safe_mode=True)
+```
+
+Then it is recommended that you change your code to read something like this:
+
+```python
+import bleach
+from bleach_whitelist import markdown_tags, markdown_attrs
+html = bleach.clean(markdown.markdown(text), markdown_tags, markdown_attrs)
+```
+
+If you are not interested in sanitizing untrusted text, but simply desire to
+escape raw HTML, then that can be accomplished through an extension which
+removes HTML parsing:
+
+```python
+from markdown.extensions import Extension
+
+class EscapeHtml(Extension):
+    def extendMarkdown(self, md, md_globals):
+    del md.preprocessors['html_block']
+    del md.inlinePatterns['html']
+
+html = markdown.markdown(text, extensions=[EscapeHtml()])
+```
+
+As the HTML would not be parsed with the above Extension, then the serializer
+will escape the raw HTML, which is exactly what happens now when
+`safe_mode="escape"`.
+
+[Bleach]: https://bleach.readthedocs.io/
+[Bleach Whitelist]: https://github.com/yourcelf/bleach-whitelist
+
+### Positional Arguments Deprecated
+
+Positional arguments on the `markdown.Markdown()` class are deprecated as are
+all except the `text` argument on the `markdown.markdown()` wrapper function.
+Using positional arguments will raise a **`DeprecationWarning`** in 2.6 and an
+error in the next release. Only keyword arguments should be used. For example,
+if your code previously looked like this:
+
+```python
+html = markdown.markdown(text, [SomeExtension()])
+```
+
+Then it is recommended that you change it to read something like this:
+
+```python
+html = markdown.markdown(text, extensions=[SomeExtension()])
+```
+
+!!! Note
+    This change is being made as a result of deprecating `"safe_mode"` as the
+    `safe_mode` argument was one of the positional arguments. When that argument
+    is removed, the two arguments following it will no longer be at the correct
+    position. It is recommended that you always use keywords when they are
+    supported for this reason.
+
+### "Shortened" Extension Names Deprecated
+
+In previous versions of Python-Markdown, the built-in extensions received
+special status and did not require the full path to be provided. Additionally,
+third party extensions whose name started with `"mdx_"` received the same
+special treatment. This behavior is deprecated and will raise a
+**`DeprecationWarning`** in version 2.6 and an error in the next release. Ensure
+that you always use the full path to your extensions. For example, if you
+previously did the following:
+
+```python
+markdown.markdown(text, extensions=['extra'])
+```
+
+You should change your code to the following:
+
+```python
+markdown.markdown(text, extensions=['markdown.extensions.extra'])
+```
+
+The same applies to the command line:
+
+```python
+python -m markdown -x markdown.extensions.extra input.txt
+```
+
+Similarly, if you have used a third party extension (for example `mdx_math`),
+previously you might have called it like this:
+
+```python
+markdown.markdown(text, extensions=['math'])
+```
+
+As the `"mdx"` prefix will no longer be appended, you will need to change your
+code as follows (assuming the file `mdx_math.py` is installed at the root of
+your PYTHONPATH):
+
+```python
+markdown.markdown(text, extensions=['mdx_math'])
+```
+
+Extension authors will want to update their documentation to reflect the new
+behavior.
+
+See the [documentation](../reference.md#extensions) for a full explanation
+of the current behavior.
+
+### Extension Configuration as Part of Extension Name Deprecated
+
+The previously documented method of appending the extension configuration
+options as a string to the extension name is deprecated and will raise a
+**`DeprecationWarning`** in version 2.6 and an error in 2.7. The
+[`extension_configs`](../reference.md#extension_configs) keyword should be used
+instead. See the [documentation](../reference.md#extension-configs) for a full
+explanation of the current behavior.
+
+### HeaderId Extension Pending Deprecation
+
+The [HeaderId][hid] Extension is pending deprecation and will raise a
+**`PendingDeprecationWarning`** in version 2.6. The extension will be deprecated
+in the next release and raise an error in the release after that. Use the [Table
+of Contents][TOC] Extension instead, which offers most of the features of the
+HeaderId Extension and more (support for meta data is missing).
+
+Extension authors who have been using the `slugify` and `unique` functions
+defined in the HeaderId Extension should note that those functions are now
+defined in the Table of Contents extension and should adjust their import
+statements accordingly (`from markdown.extensions.toc import slugify, unique`).
+
+[hid]: ../extensions/header_id.md
+
+### The `configs` Keyword is Deprecated
+
+Positional arguments and the `configs` keyword on the
+`markdown.extension.Extension` class (and its subclasses) are deprecated. Each
+individual configuration option should be passed to the class as a keyword/value
+pair. For example. one might have previously initiated an extension subclass
+like this:
+
+```python
+ext = SomeExtension(configs={'somekey': 'somevalue'})
+```
+
+That code should be updated to pass in the options directly:
+
+```python
+ext = SomeExtension(somekey='somevalue')
+```
+
+Extension authors will want to note that this affects the `makeExtension`
+function as well. Previously it was common for the function to be defined as
+follows:
+
+```python
+def makeExtension(configs=None):
+    return SomeExtension(configs=configs)
+```
+
+Extension authors will want to update their code to the following instead:
+
+```python
+def makeExtension(**kwargs):
+    return SomeExtension(**kwargs)
+```
+
+Failing to do so will result in a **`DeprecationWarning`** and will raise an
+error in the next release. See the [Extension API][mext] documentation for more
+information.
+
+In the event that an `markdown.extension.Extension` subclass overrides the
+`__init__` method and implements its own configuration handling, then the above
+may not apply. However, it is recommended that the subclass still calls the
+parent `__init__` method to handle configuration options like so:
+
+```python
+class SomeExtension(markdown.extension.Extension):
+    def __init__(**kwargs):
+        # Do pre-config stuff here
+        # Set config defaults
+        self.config = {
+            'option1' : ['value1', 'description1'],
+            'option2' : ['value2', 'description2']
+        }
+        # Set user defined configs
+        super(MyExtension, self).__init__(**kwargs)
+        # Do post-config stuff here
+```
+
+Note the call to `super` to get the benefits of configuration handling from the
+parent class. See the [documentation][config] for more information.
+
+[config]: ../extensions/api.md#configsettings
+[mext]: ../extensions/api.md#makeextension
+
+## What's New in Python-Markdown 2.6
+
+### Official Support for PyPy
+
+Official support for [PyPy] has been added. While Python-Markdown has most
+likely worked on PyPy for some time, it is now officially supported and tested
+on PyPy.
+
+[PyPy]: http://pypy.org/
+
+### YAML Style Meta-Data
+
+<del>The [Meta-Data] Extension now includes optional support for [YAML] style
+meta-data.</del> By default, the YAML deliminators are recognized, however, the
+actual data is parsed as previously. This follows the syntax of [MultiMarkdown],
+which inspired this extension.
+
+<del>Alternatively, if the `yaml` option is set, then the data is parsed as
+YAML.</del> <ins>As the `yaml` option was buggy, it was removed in 2.6.1. It is
+suggested that a preprocessor (like [docdata]) or a third party extension be
+used if you want true YAML support. See [Issue #390][#390] for a full
+explanation.</ins>
+
+[MultiMarkdown]: http://fletcherpenney.net/MultiMarkdown_Syntax_Guide#metadata
+[Meta-Data]: ../extensions/meta_data.md
+[YAML]: http://yaml.org/
+[#390]: https://github.com/Python-Markdown/markdown/issues/390
+[docdata]: https://github.com/waylan/docdata
+
+### Table of Contents Extension Refactored
+
+The [Table of Contents][TOC] Extension has been refactored and some new features
+have been added. See the documentation for a full explanation of each feature
+listed below:
+
+* The extension now assigns the Table of Contents to the `toc` attribute of
+  the Markdown class regardless of whether a "marker" was found in the
+  document. Third party frameworks no longer need to insert a "marker," run
+  the document through Markdown, then extract the Table of Contents from the
+  document.
+
+* The Table of Contents Extension is now a "registered extension." Therefore,
+  when the `reset` method of the Markdown class is called, the `toc` attribute
+  on the Markdown class is cleared (set to an empty string).
+
+* When the `marker` configuration option is set to an empty string, the parser
+  completely skips the process of searching the document for markers. This
+  should save parsing time when the Table of Contents Extension is being used
+  only to assign ids to headers.
+
+* A `separator` configuration option has been added allowing users to override
+  the separator character used by the slugify function.
+
+* A `baselevel` configuration option has been added allowing users to set the
+  base level of headers in their documents (h1-h6). This allows the header
+  levels to be automatically adjusted to fit within the hierarchy of an HTML
+  template.
+
+[TOC]: ../extensions/toc.md
+
+### Pygments can now be disabled
+
+The [CodeHilite][ch] Extension has gained a new configuration option:
+`use_pygments`. The option is `True` by default, however, it allows one to turn
+off Pygments code highlighting (set to `False`) while preserving the language
+detection features of the extension. Note that Pygments language guessing is not
+used as that would 'use Pygments'. If a language is defined for a code block, it
+will be assigned to the `<code>` tag as a class in the manner suggested by the
+[HTML5 spec][spec] (alternate output will not be entertained) and could
+potentially be used by a JavaScript library in the browser to highlight the code
+block.
+
+[ch]: ../extensions/code_hilite.md
+[spec]: http://www.w3.org/TR/html5/text-level-semantics.html#the-code-element
+
+### Miscellaneous
+
+Test coverage has been improved including running [flake8]. While those changes
+will not directly effect end users, the code is being better tested which will
+benefit everyone.
+
+[flake8]: https://flake8.readthedocs.io/en/latest/
+
+Various bug fixes have been made.  See the
+[commit log](https://github.com/Python-Markdown/markdown/commits/master)
+for a complete history of the changes.