Add Github Enterprise Support

* In addition to scope, client_options can now 
  be passed in to replace the ones hard coded
  in the gem
* Modify GET requests to use relative URLs 
  instead of absolute URLs
* Added specs to verify client_options are 
  correctly overridden and relative URLs are
  utilized

[Fixes #23]
Merge pull request #24 from jasonnoble/23_add_github_enterprise_support

Add Github Enterprise Support