zbeacon: enable sending/receiving of UDP unicast packets
selftest: disable broken zproxy_test() for now
Merge pull request #341 from mhaberler/zbeacon-unicast

zbeacon unicast UDP send/receive support
Add runtime czmq version check function
Merge pull request #342 from claws/add_runtime_version

Add runtime czmq version check function
adding ability to set front and back socket identity

moving zproxy set identity to be in every version
adding tests for zproxy set identity options
Merge pull request #343 from Talksum/master

zproxy socket identities
fix for broken identity test in zproxy
Merge pull request #345 from taotetek/master

fix for broken identity test in zproxy
Simplified zproxy

- classic complexity-oriented design! API was trying to provide a socket
  abstraction, except it wasn't an abstraction. The use of methods like
  "set frontend identity" that literally set the frontend identity,
  except via a long and complex wrapper, are a red flag. The abstraction
  should simplify, not complicate. The old API was clearly going to lead
  to endless growth (set frontend HWM, set frontend read timeout...).

- version detection was complex. I added detection for zmq_proxy_steerable
  via configure.ac.

- removed support for pre-V4 versions of libzmq, since the old zmq_proxy
  function needs no async wrapping. If zmq_proxy_steerable isn't present
  the constructor returns NULL.

- capture is moved out of the constructor since it's a minority use case.
Compiler warning/failure on libzmq 3.2
Merge pull request #346 from hintjens/master

Simplified zproxy
Cleaned up zbeacon

- unicast/send methods do not IMO belong in this class -- they are
  nothing to do with beaconing, and are instead a use of classic UDP.
- I've moved some low-level UDP methods into zsys.
- we would better IMO focus on a udp:// transport in libzmq.
- we can recreate the unicast send/recv in zsys if needed, as synchronous
  methods.
Merge pull request #347 from hintjens/master

Cleaned up zbeacon
Added comment to txp socket init, fixes #348
Selfishly added myself to AUTHORS
Merge pull request #349 from ulikoehler/fix348

Added comment to txp socket init, fixes #348
Various small fixes

- zcert had incorrect sodium.h size tests
- czmq_selftest wasn't running zproxy tests
- czmq.h didn't include zmonitor.h
Merge pull request #352 from hintjens/master

Various small fixes