Intra-host communication

Currently we have two kinds of comms:

1. inproc:// for intra-process communication with queues
2. tcp:// and tls:// for inter-process or inter-node communication with sockets

There is also a possibility in between for inter-process intra-node, that is for processes communicating to each other on the same machine but in different memory spaces.

Do we expect to see performance improvements from handling this? How expensive would this be to implement?

cc @pitrou in case he has general thoughts