change minimum version to windows vista 

Problem: integer narrowing issues.

Allow configure to support mingw64

allow host_os to accept mingw64

Problem: issue #1144, 1377

This is a silly assertion that causes problems if libzmq.dll is
called in some esoteric ways.

Solution: if the shutdown code detects WSANOTINITIALISED, then
exit silently.

Fixes #1377
Fixes #1144

Solution: add settle pause after zmq_connect

Fixes #1340

Add Bitrig to OS detection in configure.ac.

Changes the pattern for the host_os matches to *mingw* from *mingw32* to accept both mingw32 and mingw64 versions.

Fix for issue #1287: ZMQ_XPUB_NODROP documentation

#1287

fix for issue #1287

doc: add ENOENT to list of zmq_unbind error codes

Resolves zeromq/libzmq#1353

update zmq_ctx_term description for consistency

zmq_term and zmq_ctx_destroy are just aliases for zmq_ctx_term. that
being the case use 'terminate' in the description for all three so there
isn't any confusion about behavior.

also update the deprecates list in zmq_ctx_term to include
zmq_ctx_destroy.

doc: zmq_msg_init does not set errno

In fact it always returns zero.

Problem: wrong default VC rt lib for release dynamic exe.

fix CMP0053 warning with cmake 3.1

fix cmake build system

Allow zmq_msg_gets checks to assert rather than segfault

Adjust number of sent messages on hiccups

Not adjusting the sent message count may lead to situation when SUB
socket does not forward its subscriptions.

resolve #1347 addresses issue of no metadata on identity frame

Support limited metadata for STREAM sockets