Feature request: support for a self-hosted Gitlab environments

[aperez900907]

Add support for self-hosted GitLab environments.

[hunvreus]

I'm planning on adding Gitlab.com support first. Now that 0.2.0 is out, I can add more features. Once that's in, we can discuss how to support enterprise/self-hosted for GitHub/Gitlab.

Definitely interested in making this work.