solution: add x64 builds to appveyor

Solution: don't run tests on tags

This doesn't break anything, as tags was not built until now. Anyway, when building tags we really care about the release of the packages and not tests

Solution: do git pull without changing the current directoy

Solution: deploy artifcats to bintray

Implement SOCKS5 basic authentication

Fix issues with SOCKS5 proxy connection

Two issues where introduced by commit 12c4b55a:
- the proxy connection was done to the target address instead of
the proxy address
- on error the proxy connection status was not reset to unplugged

Problem: Unclear `zmq_msg_send` failure semantics

Solution: Explicitly explain message ownership semantics when the call
fails.

Fixes #3526.

Add missing information on multicasting with high data rates to PGM docs

Solution: Include a new section on configuring both ZMQ and the host
OS tx/rx buffers to facilitate sending large messages at a high data
rate with the PGM protocol.

Solution: Added relicense agreement

acinclude.m4, configure.ac: Fix several non-portable uses of `test`

Fixes #3517

Fix Fedora 30 build

Implement thread_t::setThreadName() on windows

Problem: clang-format 5 has issues with comments

Problems: typos in docs, unnecessary ifdefs, duplicated APIs

Solution: now that clang-format 6+ is used in the CI, fix it

Solution: bump CI to version 7

Solution: unify the two APIs, as they are both still in DRAFT state and
thus can be changed.

Solution: fix them

Solution: use unlikely to optimize for the most common case

Solution: remove them, only public headers have to be ifdef'd

Solution: list it

 Support XPub socket send last value caching to last subscription pipe with ZMQ_XPUB_MANUAL_LAST_VALUE. (#3511)

* Add ZMQ_XPUB_MANUAL_LAST_VALUE

* Surpport xpub send last value caching to one pipe with ZMQ_XPUB_MANUAL_LAST_VALUE

* Add test_xpubub_manual_last_value

* Add relicense and doc

Problem: Potentially unitialized variable in #3508

Solution: Create a unique endpoint for each fcn call.

Solution: Initialized it

Problem: Socket monitoring only allows ZMQ_PAIR

Solution: Allow ZMQ_PUB and ZMQ_PUSH sockets types for the monitoring.
This way someone could create a ZMQ_PULL socket connected to multiple
monitoring sockets at the same time.

Problem: PLAIN HELLO message incorrectly uses WELCOME literal

Solution: change to HELLO

Problem: signature of zmq_poller_fd does is incompatible with regular…

Solution: change return type to int (again) and return fd via an output parameter