New pagination

Update certain methods in light of: https://developer.github.com/changes/2014-03-18-paginating-method-changes/

TODO:

- [x] Gist comments
- [x] Gist commits
- [x] Gist forks
- [x] Git refs
- [x] Issue labels
- [x] Milestone labels
- [x] Organization teams
- [x] Pull request commits
- [x] Pull request files
- [x] Release assets (probably already done)
- [x] Repository collaborators
- [x] Repository contributors
- [x] Repository branches
- [x] ~~Repository downloads~~
- [x] Repository keys
- [x] Repository labels
- [x] Repository tags
- [x] Repository teams
- [x] Team members
- [x] Team repositories
- [x] User emails
- [x] User keys
  `/users/:user/keys` && `/user/keys`