Changed how rpc services register their methods.
Changed how rpc services register their methods.

This allows for some inversion of control with regard to method
registration. Now services are registered individually via a simple
interface. This is closer in design to net/rpc and gRPC, but it doesn't
rely on reflection, just a simple method that each service neesd to
implement. This allows much more flexibiliy and encapsulation than
registering methods in the rpc server constructor.

havoc-io/mutagen,havoc-io/mutagen