Allow other repository providers

[derrell]

We are implementing contrib libraries referenced by foo/bar/baz which is really a shorthand for http://github.com/foo/bar/baz. The longhand is nice, even though we may not implement it immediately, as it gives us the option of referencing an alternate location such as gitlab later. The longhand is also more clear as to what it's doing, and it allows referencing the contribs elsewhere, such as gitlab.

This is a feature request to allow the longhand.