Solution: add paragraphs to zmq_get/setsockopt man pages

Solution: add manpage

Solution: add a comment as it's easy to miss and very tempting to
"optimize"

Mingw32 Compile

Problem: Duplicated code

Solution: set_curve_key method in options_t struct with little
improvement in switch-case block

Problem: contributing guidelines unclear for new devs

Solution: port Github PR template from CZMQ

Solution: Revert "Problem: Duplicated code"

This reverts commit 022eeaf3.

Problem: Duplicated code

Solution: set_curve_key method in options_t struct with little
improvement in switch-case block

* Fixed handling of WSAEWOULDBLOCK to be generic

I don't know what was the intention of this early if statement but
now this is properly evaluated in wsa_error_no function if this is
performance issue I suggest moving evaluating this error code to the
beginning of wsa_error_no.

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

zmq_poll: only compare FD when neither item is a zmq socket

fix bug zmq4.x PUB msg to ZMTP1.0 SUB server

Problem: no mixed FD and zmq socket zmq_poll test

Solution: add one

misuse of 'close'

use 'pollset_destroy' instead of 'close' to release pollset_fd

Problem: check for item.fd causes zloop_poller regression

Solution: fix the check for the socket.
This regression happens when using zloop with zmq_pollitem_it with
only file descriptors registerted through zloop_poller.

"%" -> '%'

Add #include "precompiled.hpp"

Problem: there is no libunwind-dev on Ubuntu 14.04LTS

Solution: depend on libunwind-dev | libunwind8-dev | libunwind7-dev

Build support for VS2017, Windows SDK 10.0.14393.0, toolset v141

Fix #include case for <mstcpip.h>

On native Windows, the file system is case-insensitive, so this this
doesn't matter there.

However, when compiling on a case-sensitive filesystem, such as when
cross-compiling from a Unixoid using mingw, we have to use the case
the file is supplied with, which is all lowercase.

Problem: test_stream_exceeds_buffer fails to build on AIX

Solution: add missing includes

Solution: remove them as they are already in testutil.hpp