Git Review Integration with Github v3 Statuses API

`git review --bump` will automatically create a 'pending peer_review' status on the pull request.

The reviewer can use `git review --approve` or `git review --reject` to update the status of the pull request.  

Addresses #27 and #28

### Changelog
* Fix namespace of Thegarage::Gitx::Github module

[Github API Docs](https://developer.github.com/v3/repos/statuses/)

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