Solution: bump changelog, ABI revision, library and packaging version

Solution: add it

Problem: nuget packaging refers to imatix gsl

Solution: re-point to the maintained zeromq fork
Signed-off-by: Jim Klimov <EvgenyKlimov@eaton.com>

Problem: Jenkinsfile uses "any" agent

Solution: avoid using infrastructure and default agents by requiring a reasonable label (like in GSL and zproject)
Signed-off-by: Jim Klimov <EvgenyKlimov@eaton.com>

export ZMQ_STATIC compile flag to depending projects (MSVC)

Signed-off-by: Gunther Laure <glaure@dewetron.com>

Problem: static build broken on Win + CMake

Solution: revert the objects optimisation, and go back to building
everything twice on Windows, as the static builds needs different
preprocessor definitions from the shared one, so the objects have to be
rebuilt.
Keep the optimisation for all the other platforms.
Fixes #2858

Problem: Jenkinsfile does not pass distcheck etc.

Problem: WIN32 CMAKECONFIG_INSTALL_DIR is broken

Solution: set it to CMake instead of a subfolder of share.
See cmake find_package documentation for further info.

Problem: Debian packages are missing zmq.hpp

Problem: No Jenkinsfile

Solution: install it if available. Download it from its repo as part
of the OBS source run.
Debian and Ubuntu always ship zmq.hpp in libzmq-dev, so do the same.
In the RPM world it is in its own separate package, so don't do the
same for RPM.

Problem: DRAFT API change not in NEWS

Solution: add it

Problem: no coverage for VS2013 and VS2017

Problem: ZMQ_LINGER doc change not in NEWS

Solution: add it

Wrong ZMQ_LINGER default value

Problem: Wrong linger default value

Solution: correct documentation

Solution: use if statements to avoid building it when it's disabled

Solution: add them to Appveyor

Problems: CMake rebuilds everything twice, warnings with Tweetnacl, no autoconf option to disable Werror

Solution: add workaround until Travis really fixes the issue:
https://github.com/travis-ci/travis-ci/issues/8552

Solution: add --disable-Werror flag like the existing
--disable-pedantic or CMake's -DLIBZMQ_WERROR=OFF
Fixes #2818

Solution: build all the objects separately before the link step, to
avoid rebuilding when doing both static and shared builds

Solution: don't redefine preprocessor macro if it's already defined in
platform.hpp

Problem: accept4 not available on all platforms

Solution: check for availability in CMake and autoconf before using it

Problems: no NEWS for 4.2.3, missing some events docs, whitespace in header

Solution: add main features and bug fixes