Grouped headings in API docs

Goes with [rm/nested-headings](#) in batmanjs/batman

The grouping is a bit ugly, bit it goes like this:

- If you leave a heading plain, like `Batman.helpers`, it floats to the top
- If you give a heading with a prefix like `/api/Data Structures/Batman.Object`:
  - `api` is thrown out
  - `Data Structures` is the heading
  - `Batman.Object` is the file & title
- If you give a  heading with a prefix like `/api/Data Structures/Batman.Object/Batman.Observable`:
  - `api` is thrown out
  - `Data Structures` is the heading
  - `Batman.Object` treated as the parent for the file
  - `Batman.Observable` is the file & title

Anyways, Pics:

![screen shot 2014-02-04 at 11 10 15 pm](https://f.cloud.github.com/assets/2231765/2084880/a4cd9d52-8e34-11e3-8208-c8e3b47c0cb7.png)

It looks a little bare, but I think there are a few files waiting to be written that will fill it out:

- SetIndex, UniqueSetIndex, SetSort, Set operations
- Controller error handling
- Property / Keypath, if I can figure it out
- StateMachine

Also, I kept the search working.

@pushrax, @angelini, what do you guys think? How we doin?