Add Docs

This add the marionette docs to `/docs/:doc`. It works by connecting to middleman `config.rb` and mapping the markdown files, which would live in `source/docs` to pages on the site. 

There are still several todo items
+ add rake task for pulling in the current docs
+ add global nav for going between docs and the rest of the site
+ fix in page links (was working, isn't now)
+ show current page in the sidebar
+ additional styles

![](http://f.cl.ly/items/1H3X1u2f2P3n2T3z0b2i/Image%202014-04-13%20at%206.40.35%20PM.png)