Added two new monitoring events:
 - ZMQ_EVENT_HANDSHAKE_SUCCEED is raised once the encryption handshake succeed
 - ZMQ_EVENT_HANDSHAKE_FAILED is raised when it failed
Both events are raised on server and client side.

Solution: add most relevant bug fixes since 4.2.0

Solution: move it there, add it to src/zmq_draft.h and clarify in the
documentation and in the NEWS file that this option is not yet stable

Problem: debian build fails with automake < 1.14

Solution: create config subdir as a workaround if building the
packages with automake < 1.14

Solution: rework the bash test to avoid build failures as intended
and make it an easier one-liner

Solution: install asciidoc and xmlto in the libsodium build run, since
it already refreshes APT to download other packages, so the delay is
smaller

Solution: use packages on Ubuntu and brews on OSX. The packages and
the brews are always kept up to date, so it's no use to rebuild the
libsodium stable branch manually everytime.

Solution: Revert "Problem: Travis CI OSX builds are broken"

This reverts commit 531b3bf7.

Solution: narrow down the matrix to install valgrind and lcov only
for the test runs that use them.
CMake is part of the default image so no need to install it at all.

Solution: add it to the list

Solution: if available, call socketpair with SOCK_CLOEXEC flag to
make the process close the socket on fork+exec

Solution: if available, use eventfd with EFD_CLOEXEC flag to make
the process close the socket on fork+exec

Solution: if available, use epoll_create1 with EPOLL_CLOEXEC flag to
make the process close the socket on fork+exec

Solution: add paragraphs to zmq_get/setsockopt man pages

Solution: add manpage

Solution: add a comment as it's easy to miss and very tempting to
"optimize"

Mingw32 Compile

Problem: Duplicated code

Solution: set_curve_key method in options_t struct with little
improvement in switch-case block

Problem: contributing guidelines unclear for new devs

Solution: port Github PR template from CZMQ

Solution: Revert "Problem: Duplicated code"

This reverts commit 022eeaf3.

Problem: Duplicated code

Solution: set_curve_key method in options_t struct with little
improvement in switch-case block

* Fixed handling of WSAEWOULDBLOCK to be generic

I don't know what was the intention of this early if statement but
now this is properly evaluated in wsa_error_no function if this is
performance issue I suggest moving evaluating this error code to the
beginning of wsa_error_no.

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

* Fixed handling of WSAEWOULDBLOCK to be generic

Introduced default pointer to const char * and overrides this as NULL
if function is called by zmq::wsa_error()

zmq_poll: only compare FD when neither item is a zmq socket

fix bug zmq4.x PUB msg to ZMTP1.0 SUB server

Problem: no mixed FD and zmq socket zmq_poll test