Repo Collaborators Api Client

This is a work in progress...

See http://developer.github.com/v3/repos/collaborators/

- [x] Code (Interface and implementation
- [x] Include classes above in all relevant projects
- [x] Unit Tests
- [x] Reactive implementation

I need some feedback on one of these interface methods and its implementation.

`IRepoCollaboratorsClient.Task Add(string owner, string repo, string user);`

http://developer.github.com/v3/repos/collaborators/#add-collaborator

Documentation says this is a `PUT` statement, so I will assume you want a `Task` as the return statement? (Similar to the `DELETE` statement)

If so - the PUT statement would require an overload like the Delete statement?

`ApiConnection.Delete(endpoint);`
`ApiConnection.Put(endpoint);`

Let me know if this is fine I will add the method.

Thanks