Added test and doc section for ZMQ_SHARED message flag

Added ZMQ_SHARED message option to zmq_msg_get()

Add Docker support

Ensure EOL is present at end of utils file.

MacOS/Clang complain due to presence of -Wnewline-eof in CZMQ.

Code cleanup

Add test for unbinding inproc socket.

Resolve issue #949

Windows: if WSA error number is held, use directly.

It must be done this way, as WSAGetLastError returns 0 in these circumstances

vs2012: Add missing socks files

Don't delay reception of signal

- new code may help undersdtand issue #1108
  (https://github.com/zeromq/libzmq/issues/1108)
- code cleanups

Fix to build on OpenBSD

Add static compilation on CMake

Thread scheduling parameters: Use ZMQ context options instead of environment variables.

environment variables.

Code cleanup

Problem: two header files for a single library

Add missing socks files

socks: fix build on FreeBSD

The fix should be sane on all UNIX-like systems, so there's
no ZMQ_HAVE_FREEBSD involved.  It's likely that other BSDs
stumble across this problem too.

Solution: fixed this. Also minor code cleanups.

Users who need e.g. zmq_curve_keypair() have to remember to include
zmq_utils.h, which is counter-intuitive. The whole library should be
represented by a single include file.

Solution: merge all contents of zmq_utils.h into zmq.h, and deprecate
zmq_utils.h. Existing apps can continue unchanged. New apps can ignore
zmq_utils.h completely.

Problem: zmq_msg_gets did not set errno on unknown properties

Solution: set errno to EINVAL when a property does not exist.

Also fixed test_metadata.cpp to test this case.