Problem: coverage includes tweetnacl, which is not our code

Solution: exclude tweetnacl from coverage

Problem: insufficient tests for zmq_timers_* and inadequate behaviour in corner cases

Solution: add test

Problem: missing tests for zmq_timers_* corner cases, missing handling of such corner cases, code duplication, missing assertions in test code

Solution: add tests, add checks to timers_t, add match_by_id functor, add assertions

Solution: added tests

Solution: replace sleep_ my msleep

Problem: insufficient tests for zmq_poller_*

Problem: replaced by assertions resp. removed

Solution: added test cases

Solution: add test case

Solution: replace ETIMEDOUT within socket_poller_t and all client code by EAGAIN

Fixes #2713

Solution: Return EBADF instead

Problem: calling zmq_poller_wait* with NULL events causes an assertion, as opposed to other NULL arguments, which return an error

Solution: return EFAULT when such an operation is attempted

Solution: return EFAULT when such an operation is attempted

Problem: missing test cases for zmq_poller_* functions called with invalid arguments and corner cases for zmq_poller_wait_*

Solution: added test cases

Solution: add checks, added test cases

Solution: added test cases

Problem: no tests for socket-related functions passing NULL as socket

Soluton: added tests

Problem: code duplication within zmq::select_t::rm_fd

Solution: extract find_fd_entry_by_handle from rm_fd

Problem: packages builds not mentioned in README.md

Problem: test_monitor fails sometimes due to a wrong event received but unclear which one

Solution: add brief description and links

Solution: enable test

Solution: add diagnostic output

Problem: no tests for client-side events for successful handshake and authentication failure in handshake

Problem: test_zap_unsuccessful_status_500 and test_curve_security_with_bogus_client_credentials sometimes fail, particulary on slow/valgrind runs

Solutio: relax test assertion

Problem: no tests for client-side events for successful handshake and authentication failure in handshake

Solution: added tests for CURVE, add emitting of client-side event in curve_client_t; add ZAP code 300/500 tests for all mechanisms; suppress sending an error message for ZAP code 300

Problem: test_security_gssapi expects wrong event

Solution: do it to avoid leaks. Even though they are below 33 bytes so
it's all allocated on the stack, the small message size might change in
the future.

Solution: fix it

Problem: test_sockopt_hwm fails occasionally

Solution: relaxed assertion to accept 10% of the SNDHWM, and updated documentation accordingly

Solution: align assertions with specification of ZMQ_SNDHWM (actual number of enqueueable messages may be lower)

Problem: RPM -devel still ships libzmq.la

Solution: mention recent changes

Solution: don't. libtool's archive files are already being deprecated
in Debian-based distros. They are no longer necessary, and cause the
reverse dependencies to over-link.
EG: when built with sodium/pgm/krb5, all applications/libraries
linking against libzmq would be forced to link against sodium/pgm/krb5
despite not using any of those libraries symbols.

Problems: GSSAPI builds broken with picky compilers, Debian/RPM packages do not use GSSAPI, no CI jobs that test GSSAPI