Register and Tag Sunlight.jl

The [Sunlight Foundation](http://sunlightfoundation.com/api/) has a bunch of really cool APIs that I've been trying to use. This package is designed to be an umbrella for all of them, but so far I've only implemented the [Influence Explorer API](http://sunlightlabs.github.io/datacommons/) (which has -frankly- a huge set of methods).