Nicedocs

Addresses https://github.com/mapbox/tm2/issues/462 -

![2014-06-26 16_52_13](https://cloud.githubusercontent.com/assets/108094/3404661/c643c6d8-fd73-11e3-90b0-9e2750e83023.gif)

Realized that we really do need a manual and cutting it isn't sufficient. Linking to online docs is a bad idea at this point, because there aren't any.

One nice this about this is that it saves your tab state - often I find myself _either_ wanting to look at fonts a lot _or_ carto reference a lot - so this is now more convenient.

- [ ] Now that I have a layout pinned down, I'm going to work on cleaning up the actual manual. This might need a more focused experience.
- [ ] Cleanup walkthrough to match design changes

@yhahn you see promise in this direction?