add the Lita::Handlers::GithubRepo handler

This handler is designed to handle the usual Repository operations. More features will be added later, but it currently supports:

* create
* delete
* info (show some details of repo)

There were also some bug fixes:

Fix some problems with the Regexes found during testing. The regexes were fixed, the tests were improved to fail more reliably, and specific tests for the failure conditions were added.

In addition to the new handler, some LitaGithub modules were introduced to de-dupe some frequently used code.