Beam: a simple stream-oriented communication protocol for distributed systems.

This patch includes a stripped down implementation with a bare minimum
unix socket transport. It relies on fd passing for stream multiplexing.

The purpose of this first patch is to allow implementation of dynamic
linking, which will allow advanced service discovery.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)
Beam: convenience functions Listen and Connect

These convenience functions expose a familiar face to the unknown and bizarre world of beam networking.

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)