Expose the DefaultRequestHandler to rest engines not using your "main" or "bind".

So, I have an existing multi-protocol netty based engine that I'd like to throw a rest processor on top of. I just need to be able to add the request handler to my existing pipeline, but did not see how that could be done with the existing bind function. Here's my proposed patch, let me know if you're willing to accept it.

The "bind" function in RestExpress did not allow me to take the handler and add it to my own pipeline (outside of a system that traditionally holds it's own "main").