Solution: re-enable them

Add poller docs

Solution: add symlinks to zmq_poller.txt

Solution: add initial documentation

Solution: return NULL and set errno to ENOMEM

Solution: change comment, and add test case for zmq_poller_modify with events == 0

Problem: inconsistent behaviour of zmq_poller_add and zmq_poller_add_fd in case of memory exhaustion

Solution: always return -1 with errno == ENOMEM

ZMTP 3.1 PING Context not implemented

Solution: migrate to unity assertions

Solution: if a PING message contains a context, echo it back in the
PONG message. In order to do so, create the PONG message when PING
is received and store it in the engine.
After the PING the engine goes straight to encoding and sending, so
there can always be at most one pending PING.
Add tests for various contexts.

Solution: treat the first byte of the command body as the size of the
command name, rather than as an id, to comply with ZMTP 3.1.
This was not an actual problem at runtime since both heartbeat
commands have a size of 4, which was treated like an id.
But once SUBSCRIBE/UNSUBSCRIBE get implemented it needs to be checked.

Solution: remove it, it doesn't add much value anyway

Solution: migrate to unity

Problem: building on Linux with Sun Studio still fails

Solution: initialise it

Solution: add compiler flags to support extensions like anonymous
structs in unions, fix casting of const, and check for suncc rather
than solaris

Problem: no way to specify source interface for UDP multicast sender …

Solution: if a binding interface is provided in the sender URL we pass
it to IP[V6]_MULTICAST_IF setsockopt

Problem: test_radio_dish triggers aliasing errors with some compilers

Solution: refactor the test code to work around aliasing issues

Problem: build broken on Solaris with Sun Studio compilers

Solution: change the ifdef to always print on any Unix, as they
all have ulimit

Solution: use a different max socket value on Solaris, where the
default limit is 256 instead of 1024

Solution: add missing const qualifier to internal functions

Solution: do it explicitly to fix build on Solaris 10/11 with the Sun
compiler

Solution: remove constness on pair arguments. Fixes #3090

Problem: warnings in MSVC builds around size_t/int

Solution: use proper types

Problem: getrandom test does not check if it's working

Problem: ZMQ doesn't expose the MULTICAST_LOOP socket option

Solution: update to document new binding options and IPv6 support

Solution: add a new ZMQ_MULTICAST_LOOP option for UDP sockets.

Problem: test helper recv_string_expect_success ignores flags

Solution: pass the flags to zmq_recv

UDP Ipv6 support

Solution: Add IPv6 support

Solution: check return value in autoconf and CMake. On some platforms
the function is available but not implemented (eg: GNU/Hurd).

Add ip_resolver.cpp and ip_resolver.hpp for vs2015 libzmq project

acinclude.m4: check if -latomic is needed.