Solution: add monitor event socket option

Solution: added it

Solution: extract common base class stream_listener_base_t

Solution: extract common base class stream_connecter_base_t

Solution: detect cacheline size for aligment purposes at build time
instead of hard-coding it, so that PPC and S390 can align to a value
greater than the 64 bytes default.
Uses libc getconf program, and falls back to the previous value of 64
if not found.

Solution: bump ABI and revisions and changelog now that v4.3.1 is out

Solution: use requires.private, which pkg-config expands recursively
so that dependencies of dependencies can be linked against when
using pkg-config --static

Solution: use the same for both autotools and cmake

Solution: bump to 5.2.1 and 4.3.1 respectively

Solution: bump it to 5.2.0 as new stable APIs have been added

* Add specific option to select radix tree implementation for subscriptions (defaults to ON if draft API enabled).

* Problem: radix tree needs benchmarks and improvements

Solution: add a benchmark and make suggested improvements

- MacOS version requires CMake version 3.0.2 (because of policy CMP0042)
- Add option to build instrumented binaries with Address Sanitizer
- Add option to select compiler intrinsics for atomic ops
- Only build docs on request (saves build time)

subscriptions increases

Solution: use a radix tree instead of a trie to store subscriptions

- Lowercase all commands
- Unify indent to 2 spaces
- Remove spaces around brackets
- Remove repitition of condition in else(...) and endif(...)

Note: (re-)running CMake did not change the content of the generated files

Solution: apply the same commadn for RelWithDebInfo build

* Problem: No CI for mingw64

Adding CI support for mingw64 to appveyor.yml

Reason: To help address the issue:
  Several checks fail under 64-bit MinGW on Windows when running make check #3185

* Problem: Docs do not build with mingw64, dll already in right place

Turning off WITH_DOC for mingw64
Removing copy command for mingw64 and cygwin64 (it now seems to be directly built in "bin" directoy)

Solution: avoid exporting targets and installing files if neither
BUILD_SHARED nor BUILD_STATIC is set

Solution: Use cmake's libdir variable to ensure that the pkgconfig file
ends up in the correct lib/lib64 directory. This matches the autotools
behaviour.

This commit ensures that the variable CMAKE_*_OUTPUT_DIRECTORY
are considered when creating the library.

Setting EXECUTABLE_OUTPUT_PATH and LIBRARY_OUTPUT_PATH variables is deprecated

Solution: do not check for windows.h on cygwin

Solution: move to separate header

Solution: add compile check

Solution: extract constants / move to plain_common.hpp

Solution: ignore tautological-constant-compare warnings, as they
might be useless on 64 bit but they are not on 32 bit where sizeof
size_t != sizeof uint64_t

Solution: Enable VS static analyzer and core guideline checks

Solution: skip tests than can never succeed with MSVC

Solution: Use wepoll on Windows

Problem: API poller cannot be set independently from I/O thread poller, poll I/O thread poller broken on Windows

Solution: change platform definitions to separate API poller from I/O thread poller, disallow configuring poll I/O thread poller on Windows

Solution: enable warnings-as-errors

Solution: Factor the code into a different file with a well defined API and add
unit tests.

Solution: set the equivalent flag

Problem: When building libzmq with CMake, the installed libzmq.dylib
  has a relative install name (otool -D libzmq.dylib) on MacOS. This
  is a regression against building via autotools which sets an
  absolute install name. Effectively, the CMake built libzmq.dylib
  is rendered useless if installed in non-system directories and
  used in environments without explicit DYLD_LIBRARY_PATH mgmt. For
  example running any of the installed executables currently fails:
  $ /some_install_prefix/bin/inproc_lat
  dyld: Library not loaded: libzmq.5.dylib
    Referenced from: /some_install_prefix/bin/inproc_lat
    Reason: image not found
  Trace/BPT trap: 5

Solution: Best practice is to install relocatable dylibs.
  On MacOS this means setting an install name with a special prefix,
  e.g. @rpath/libzmq.dylib, and adding the relevant search paths
  to the embedded rpath list. In this patch the necessary CMake options
  are added to generate the desired relocatable dylibs. Find more
  information on: https://cmake.org/Wiki/CMake_RPATH_handling.

* Fixes issues with the PDB install rule for VS solutions

* Fix for compile PDB and linker PDB under Windows

Solution: revert the revert!

Revert "Problem: regression in 4.2.3 went unnoticed, want to release 4.2.5"

This reverts commit 5f17e26f.

Fixed gcc-related build problem resulting from `-errwarn=%all` switch.

Fixes #3012.