Import zeromq-4.0.3 as wip/zeromq.

The 0MQ lightweight messaging kernel is a library which extends the
standard socket interfaces with features traditionally provided by
specialised messaging middleware products. 0MQ sockets provide an
abstraction of asynchronous message queues, multiple messaging
patterns, message filtering (subscriptions), seamless access to
multiple transport protocols and more.
+zeromq (4.0.3)