problem: not all configurations were built (and some were duplicated) in
Windows CI
solution: add all correct combinations to appveyor.yml

problem: cmake added a prefix of lib to libzmq, resulting in
liblibzmq.so
solution: set an empty prefix

CTest: add all sources in tests folder to CTest

TweetNaCL: add windows randombytes implementation

CMake: use libsodium + add Windows CI

problem: zmq_pollfd is not needed anymore when zmq_poller in place.

problem: ZMQ_POLLER doesn't support polling on out

enable static libraries on mingw

honor buffer reference count in zmq::shared_message_memory_allocator:…

problem: polling on multiple sockets is complicated

Fixed for issue  #1315

fix a typo in ypipe.hpp

Fixes issue #1556

Issue 1588 : Rollback in case send fails for multipart msg

create signaler::recv_failable()

In real world usage, there have been reported signaler failures where the
eventfd read() or socket recv() system call in signaler::recv() fails,
despite having made a prior successful signaler::wait() call.

this patch creates a signaler::recv_failable() method that allows
unreadable eventfd / socket to return an error without asserting.

fix error with gcc 5.2

Solution: full is if number of msg is greater than hwm, not greater than hwm - 1