First implementation of minimal Broker API

Yep, and tcp incurs all kinds of nasty overhead compared to a local, lock-free queue. What's wrong with exposing this on the API as part of the URI (just as ZMQ does anyway or every single browser for that matter), e.g. "tcp://...", "inproc://...", "mpi://...", "asio://..."? This can even be used to select the underlying transport implementation.