`grunt doc` generates html documentation in doc/

We have a lot of JSDoc-style comments, but we don't do anything with them. This branch adds a `grunt doc` command that compiles our typescript files into html. This can be accessed from `doc/index.html`. Here's a preview:

![screen shot 2014-06-05 at 1 58 08 pm](https://cloud.githubusercontent.com/assets/3344958/3193625/b398b000-ecf4-11e3-874b-319b89f40a9a.png)

Note that after checking out this branch, you'll have to `npm install && grunt doc && open doc/index.html`.

In the future, we could have these pages hosted by github or something.