Problem: can't process ZMTP 3.1 cancel/subscribe commands

Solution: add some msg helpers to parse commands, and check for
subscribe or cancel commands and process them accordingly in the xpub
and xsub classes.

Solution: use the --version-script map on those systems as well, as it
is supported

Solution: do it to silence static analysis warnings

Solution: fix path in Makefile.am

Solution: list them

* update pair doc

Fix clang-tidy configuration

Solution: add missing quotation marks

Solution: use correct double quotes

* Problem: connecter classes do not handle ZMQ_RECONNECT_IVL of -1

Solution: Add guards to prevent a reconnect timer from starting if ZMQ_RECONNECT_IVL is -1
(Issue 3158)

Problem: epoll_t employs an unnecessary mutex

Solution: remove the mutex

use cmake compile the unittest

Add cygwin64 CI on Appveyor

wepoll integration fixes

Solution: rename it

Solution: add them so that they get included in "make dist"

Solution: allow failure of cygwin64 build

Solution: do not check for windows.h on cygwin

Solution: add cygwin build

Problem: not able to use wepoll in configure script

Solution: add wepoll as a polling system

* fix computation of winsock fd_set size

Resolve huge stack size requirements problem with select on Windows

Solution: removed obsolete information

Solution: use resizable_optimized_fd_set_t

Solution: remove duplicated code

Solution: use optimized_fd_set_t

Solution: use it

Solution: move to separate header

Solution: guard CMake statement properly

Solution: switch one build to non-draft

Solution: use fast_vector_t as in poll implementation

Solution: unify between Windows and non-Windows code

Solution: extract to function

Solution: extract class template fast_vector_t

Solution: extract compute_timeout method

Solution: remove duplication