[WIP][waiting-feedback] Add GitLab support.

[cirosantilli]

With this I can do:

var Octokit = require('octokit')
var gh = Octokit.new({
  api: 'gitlab',
  token: '0123456789'
})
var repo = gh.getRepo('cirosantilli', 'test')
repo.getInfo().then(function(repo) {
  console.log(repo)
  console.log(repo.name)
})

If you think I'm going in the right direction I will continue to implement as much of GitLab as possible in this manner, and add tests.

The goal is to:

• keep the GitHub part unaltered.
• allow the same interface to interact with both websites by converting GitHub input URLs GitLab's, and GitLab's output JSON to their GitHub analogues. E.g.:
  • GitHub URL /repos/:user/:name becomes GitLab /projects/#{user}%2F#{repo}
  • GitLab's .path reply field becomes is converted to it's GitHub analogue .name, and .name which is the humanish name is converted to a new identifier humanName.
    This is simplistic, but works for many fields.

I felt that implementing it here was simpler than at https://github.com/philschatz/octokat.js because in my mind this is a perfect case for using inheritance to model the situation, and Octokat has no explicit methods that can be polymorphed.