Add nanomsg to third_party, with some demos.

Add nanomsg to third_party, with some demos.

This isn't something I want to make part of Skia, but just a substrate to build cross-process demos on top of.  If I client were to use Skia cross-process, they'd drop their own IPC system in here.

If you're not familiar, nanomsg (nanomsg.org) is the next-gen zeromq (zeromq.org), from the same author, righting all his design wrongs from zeromq.

It's a lot like the lower half of mojo, dealing with making the connections and getting messages reliably from A to B.  Think, better sockets, and it spans nicely across in-process (with zero-copy), inter-process, and TCP.

BUG=skia:
R=bsalomon@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/294873004