Migrate documentation to MkDocs proper

This is still a bit of a work in progress, but throwing it up so people can see and provide feedback if they want.
Agree re. MkDocs and happy to follow up on that - make sure to keep `@tomchristie`'ing me on any thread related to that.

On this specfic issue, it should be in the menu, and is currently listed under 'topics'... http://www.django-rest-framework.org/topics/kickstarter-announcement and 
![screen shot 2014-10-23 at 09 23 59](https://cloud.githubusercontent.com/assets/647359/4750066/f655d1f0-5a8d-11e4-90d8-4ca9f50b1c61.png)