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, 0 insertions, 126 deletions

diff --git a/docs/extensions/header_id.txt b/docs/extensions/header_id.txt
deleted file mode 100644
index 5557b1b..0000000
--- a/docs/extensions/header_id.txt
+++ /dev/null
@@ -1,126 +0,0 @@
-title:      HeaderId Extension
-prev_title: CodeHilite Extension
-prev_url:   code_hilite.html
-next_title: Meta-Data Extension
-next_url:   meta_data.html
-
-HeaderId
-========
-
-Summary
--------
-
-The HeaderId extension automatically generates `id` attributes for the header
-elements (`h1`-`h6`) in the resulting HTML document.
-
-This extension is included in the standard Markdown library.
-
-!!! warning
-    This extension is **Pending Deprecation**. The [Table of Contents][toc]
-    Extension should be used instead, which offers most the features of this
-    extension and more.
-    
-[toc]: toc.html
-
-Syntax
-------
-
-By default, all headers will automatically have unique `id` attributes 
-generated based upon the text of the header (see below to turn this off). 
-Note this example, in which all three headers would have the same `id`:
-
-    #Header
-    #Header
-    #Header
-
-Results in:
-
-    <h1 id="header">Header</h1>
-    <h1 id="header_1">Header</h1>
-    <h1 id="header_2">Header</h1>
-
-Usage
------
-
-See [Extensions](index.html) for general extension usage, specify `markdown.extensions.headerid`
-as the name of the extension.
-
-See the [Library Reference](../reference.html#extensions) for information about
-configuring extensions.
-
-The following options are provided to configure the output:
-
-* **`level`**: Base level for headers.
-
-    Default: `1`
-
-    The `level` setting allows you to automatically adjust the header levels to
-    fit within the hierarchy of your HTML templates. For example, suppose the 
-    markdown text for a page should not contain any headers higher than level 3
-    (`<h3>`). The following will accomplish that:
-
-        >>>  text = '''
-        ... #Some Header
-        ... ## Next Level'''
-        >>> from markdown.extensions.headerid import HeaderIdExtension
-        >>> html = markdown.markdown(text, extensions=[HeaderIdExtension(level=3)])
-        >>> print html
-        <h3 id="some_header">Some Header</h3>
-        <h4 id="next_level">Next Level</h4>'
-
-* **`forceid`**: Force all headers to have an id.
-
-    Default: `True`
-
-    The `forceid` setting turns on or off the automatically generated ids for 
-    headers that do not have one explicitly defined (using the
-    [Attribute List](attr_list.html) extension).
-
-        >>> text = '''
-        ... # Some Header
-        ... # Header with ID # { #foo }'''
-        >>> html = markdown.markdown(text,
-                                     extensions=['markdown.extensions.attr_list',
-                                                 HeaderIdExtension(forceid=False)])
-        >>> print html
-        <h1>Some Header</h1>
-        <h1 id="foo">Header with ID</h1>
-
-* **`separator`**: Word separator. Character which replaces white space in id.
-
-    Default: `-`
-
-* **`slugify`**: Callable to generate anchors.
-
-    Default: `markdown.extensions.headerid.slugify`
-
-    If you would like to use a different algorithm to define the ids, you can
-    pass in a callable which takes two arguments:
-
-    * `value`: The string to slugify.
-    * `separator`: The Word Separator.
-
-Using with Meta-Data
---------------------
-
-The HeaderId extension also supports the [Meta-Data](meta_data.html) extension.
-Please see the documentation for that extension for specifics. The supported 
-meta-data keywords are:
-
-* `header_level`
-* `header_forceid`
-
-When used, the meta-data will override the settings provided through the  
-`extension_configs` interface. 
-
-This document:
-
-    header_level: 2
-    header_forceid: Off
-
-    # A Header
-
-
-Will result in the following output:
-
-    <h2>A Header</h2>