Add RemoveListener for root emitter

[bartversluijs]

This'll add the 'RemoveListener' function for the root emitter. You can remove listeners when you create a new emitter, but this library supports an emitter out of the box, I like to call it the 'root' emitter.

There was no way to remove listeners on that emitter in a simple way. And most functions have a wrapper foor the root emitter. So I've created one for the RemoveListener.