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, 110 insertions, 0 deletions

diff --git a/docs/extensions/meta_data.md b/docs/extensions/meta_data.md
new file mode 100644
index 0000000..36d5e7a
--- /dev/null
+++ b/docs/extensions/meta_data.md
@@ -0,0 +1,110 @@
+title: Meta-Data Extension
+
+Meta-Data
+=========
+
+Summary
+-------
+
+The Meta-Data extension adds a syntax for defining meta-data about a document.
+It is inspired by and follows the syntax of [MultiMarkdown][]. Currently,
+this extension does not use the meta-data in any way, but simply provides it as
+a `Meta` attribute of a Markdown instance for use by other extensions or
+directly by your python code.
+
+This extension is included in the standard Markdown library.
+
+[MultiMarkdown]: http://fletcherpenney.net/MultiMarkdown_Syntax_Guide#metadata
+
+Syntax
+------
+
+Meta-data consists of a series of keywords and values defined at the beginning
+of a markdown document like this:
+
+```md
+Title:   My Document
+Summary: A brief description of my document.
+Authors: Waylan Limberg
+         John Doe
+Date:    October 2, 2007
+blank-value:
+base_url: http://example.com
+
+This is the first paragraph of the document.
+```
+
+The keywords are case-insensitive and may consist of letters, numbers,
+underscores and dashes and must end with a colon. The values consist of
+anything following the colon on the line and may even be blank.
+
+If a line is indented by 4 or more spaces, that line is assumed to be an
+additional line of the value for the previous keyword. A keyword may have as
+many lines as desired.
+
+The first blank line ends all meta-data for the document. Therefore, the first
+line of a document must not be blank.
+
+Alternatively, You may use YAML style deliminators to mark the start and/or end
+of your meta-data. When doing so, the first line of your document must be `---`.
+The meta-data ends at the first blank line or the first line containing an end
+deliminator (either `---` or `...`), whichever comes first. Even though YAML
+deliminators are supported, meta-data is not parsed as YAML.
+
+All meta-data is stripped from the document prior to any further processing
+by Markdown.
+
+Usage
+-----
+
+See [Extensions](index.md) for general extension usage, specify
+`markdown.extensions.meta` as the name of the extension.
+
+Accessing the Meta-Data
+-----------------------
+
+The meta-data is made available as a python Dict in the `Meta` attribute of an
+instance of the Markdown class. For example, using the above document:
+
+```pycon
+>>> md = markdown.Markdown(extensions = ['markdown.extensions.meta'])
+>>> html = md.convert(text)
+>>> # Meta-data has been stripped from output
+>>> print html
+<p>This is the first paragraph of the document.</p>
+
+>>> # View meta-data
+>>> print md.Meta
+{
+'title' : ['My Document'],
+'summary' : ['A brief description of my document.'],
+'authors' : ['Waylan Limberg', 'John Doe'],
+'date' : ['October 2, 2007'],
+'blank-value' : [''],
+'base_url' : ['http://example.com']
+}
+```
+
+Note that the keys are all lowercase and the values consist of a list of
+strings where each item is one line for that key. This way, one could preserve
+line breaks if desired. Or the items could be joined where appropriate. No
+assumptions are made regarding the data. It is simply passed as found to the
+`Meta` attribute.
+
+Perhaps the meta-data could be passed into a template system, or used by
+various Markdown extensions. The possibilities are left to the imagination of
+the developer.
+
+Compatible Extensions
+---------------------
+
+The following extensions are currently known to work with the Meta-Data
+extension. The keywords they are known to support are also listed.
+
+* [HeaderId](header_id.md)
+    * `header_level`
+    * `header_forceid`
+* [WikiLinks](wikilinks.md)
+    * `wiki_base_url`
+    * `wiki_end_url`
+    * `wiki_html_class`