Updated to use v2 of GitHub API

* Updated current API methods to use the latest version (V2) of the API
* Added a few new functionality
   * using the Tree & Blob API that are still at the beginning phases)
   * ability to search for a user based on either their name or email (this one is tricky because the API gives two different structured hash. the email gives the same has as .user method but the username gives a different hash.

I am still new to OSS contributions and Ruby in general so if there are obvious things that I missed, please let me know. I have tried to emulate the style the previous version of the API was written and made sure at least the gem's API is backwards compatible with the update to v2 of GitHub API.