Docstring and Sphinx support

closes #3 

This adds a ton of documentation, as well as support for Sphinx, which compiles documentation to an HTML website.

![screen shot 2014-10-10 at 1 56 49 pm](https://cloud.githubusercontent.com/assets/2433509/4596762/d5e8f1ae-50a6-11e4-9ef5-64fa7fe367f8.png)

What's the difference between `ends_on` and `ends_after` here? If it's specified in more detail in another file can we note that?