Update library to allow for GitHub Enterprise URLs.

The base URL for a GitHub Enterprise account is obviously different. But
there's also a slight difference with the API URL as well.
Add tests and update travis.yml to build from tip.

The way that this library was built it wasn't hard to add in a separate
endpoint to connect to. Additionally added travis.yml to build (but
allow failures) from the tip of the Go build so we can be sure we're
fine for the next release.
Remove this from license.
Merge pull request #3 from johnbellone/master

GitHub Enterprise Support