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, 39 insertions, 0 deletions

diff --git a/docs/extensions/smart_strong.md b/docs/extensions/smart_strong.md
new file mode 100644
index 0000000..1fb3c68
--- /dev/null
+++ b/docs/extensions/smart_strong.md
@@ -0,0 +1,39 @@
+title: Smart Strong Extension
+
+Smart_Strong
+============
+
+Summary
+-------
+
+The Smart_Strong extension adds smarter handling of double underscores within
+words. This does for double underscores what [smart_emphasis][] does for single
+underscores.
+
+The Smart_Strong extension is included in the standard Markdown library.
+
+[smart_emphasis]: ../reference.md#smart_emphasis
+
+Example
+-------
+
+```pycon
+>>> import markdown
+>>> markdown.markdown('Text with double__underscore__words.', \
+                      extensions=['markdown.extensions.smart_strong'])
+u'<p>Text with double__underscore__words.</p>'
+>>> markdown.markdown('__Strong__ still works.', \
+                      extensions=['markdown.extensions.smart_strong'])
+u'<p><strong>Strong</strong> still works.</p>'
+>>> markdown.markdown('__this__works__too__.', \
+                      extensions=['markdown.extensions.smart_strong'])
+u'<p><strong>this__works__too</strong>.</p>'
+```
+
+Usage
+-----
+
+See [Extensions](index.md) for general extension usage, specify
+`markdown.extensions.smart_strong` as the name of the extension.
+
+This extension does not accept any special configuration options.