User documentation

[mrocklin]

It would be nice to have user facing documentation, even if it's just API docs.

I use and recommend readthedocs/sphinx. It's very easy to get set up.

[insertinterestingnamehere]

Right. I've spent some time working on integrating Doxygen into Sphinx using Breathe. It's sort-of working now, but still needs some work. More on this soon.