doc: update style for iojs

* updates the styling for the iojs docs
* pulls the processing step for markdown files into
  a separate module
* adds the ability to insert comments into the markdown

PR-URL: https://github.com/iojs/io.js/pull/297
Fixes: https://github.com/iojs/iojs.github.io/issues/23


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>