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, 52 insertions, 0 deletions

diff --git a/docs/extensions/definition_lists.md b/docs/extensions/definition_lists.md
new file mode 100644
index 0000000..e9f8984
--- /dev/null
+++ b/docs/extensions/definition_lists.md
@@ -0,0 +1,52 @@
+title: Definition Lists Extension
+
+Definition Lists
+================
+
+Summary
+-------
+
+The Definition Lists extension adds the ability to create definition lists in
+Markdown documents.
+
+This extension is included in the standard Markdown library.
+
+Syntax
+------
+
+Definition lists are defined using the syntax established in
+[PHP Markdown Extra][php].
+
+[php]: http://www.michelf.com/projects/php-markdown/extra/#def-list
+
+Thus, the following text (taken from the above referenced PHP documentation):
+
+```md
+Apple
+:   Pomaceous fruit of plants of the genus Malus in
+    the family Rosaceae.
+
+Orange
+:   The fruit of an evergreen tree of the genus Citrus.
+```
+
+will be rendered as:
+
+```html
+<dl>
+<dt>Apple</dt>
+<dd>Pomaceous fruit of plants of the genus Malus in
+the family Rosaceae.</dd>
+
+<dt>Orange</dt>
+<dd>The fruit of an evergreen tree of the genus Citrus.</dd>
+</dl>
+```
+
+Usage
+-----
+
+See [Extensions](index.md) for general extension usage, specify
+`markdown.extensions.def_list` as the name of the extension.
+
+This extension does not accept any special configuration options.