Updated libraries, added Markdown Extra, and changed config options.

* Updated the existing libraries to the latest versions:
  * Markdown: 1.0.1p from January 23, 2013
  * Smartypants: 1.5.1f from January 23, 2013

Added Markdown Extra so that decent code blocks are available. With
this, an extra option has been added to the configuration options
that lets you choose Extra.

Other updates include:
* dropping Wordpress specific information from both Markdown libs
* updated NOTICE with latest license information from Michel Fortin