Callbacks currently expect a result to be returned every time. This isn't the case however with things such as git_status_foreac_ext.

Also, the code that is looking for a return value currently doesn't work and we'll need tbranyen/combyne#65 fixed before it works properly.

Additionally we'll need callbacks to handle having their own payloads instead of a universal payload that's sent to each callback. This is stopping the inclusion of many methods that use this pattern.