Doc stylesheet

Haven't worked out how to hook this up yet - probably just append to codo.css using grunt or something. Anyway, to get this under source control here's a PR ;)

To use this, append to codo.css

Preview:
![image](https://f.cloud.github.com/assets/4961726/1198141/d3c87ebe-24ef-11e3-86a0-c73f698f1666.png)