Feature request: Add support for additional git remotes.

Git remotes are useful for team collaboration. This pull request supports the following structure for adding additional remotes.

```JSON
{
  ...
  "repository": {
    "uri": "git@github.org:draenen/mysite.git",
    "revision": "master",
    "remotes": {
      "developer2": "git@github.org:developer2/mysite.git"
    }
  }
}
```