Change XSUB -> XPUB multipart message processing.

Now only the first part in a multipart message will be treated as subscribe/unsubscribe.
The rest will be considered user messages regardless of the first byte.

Allow library output name to be changed externally

Remove the superfluous build requirement of libsodium-devel

problem: test_wss_transport keys expired

Solution: generate new keys that last for 100 years

Problem: test_pair_tcp_cap_net_admin requires sudo but is enabled by …

Problem: WSAEventSelect checks for FD_OOB, but select does not

WSAEventSelect is used on Windows (when select is the polling method)
only if waiting for more than one socket family, excluding IPv4/6.
It is then passed FD_OOB, which means it can be woken by OOB messages,
but select later on never checks for it.
Remove FD_OOB as it's not actually used for anything.

Fix typo in email address

Problem: Poller example has wrong argument order

Solution: flipped arguments in example

Solution: add an option to enable it, and default to false. Enable it in
the CI so we don't lose coverage, as it works on Travis.

Fixes #3725

Problem: ipc transport not supported under Windows

Solution: call tune_socket only if connect was successful

Solution: implement support

Add a few quality of life improvements to the Android build scripts

Problem: libzmq-dev not installable with libczmq-dev on Ubuntu 16.04

Solution: add alternative dependency as libgnutls-dev | libgnutls28-dev,
so that the resolver can break the tie, as libcurl4-nss-dev depends on
libgnutls-dev which conflicts with libgnutls28-dev

Problem: Android build script is severely outdated

Solution: Migrate build scripts from Android NDK r11c to r20.
- Standalone toolchain
- Migration from GCC to Clang
- Migration from libgnustl to libc++
- Dropped support for API level below 16 (Android 4.1), previously it was API level 9 (Android 2.3)
- Dropped support for mips architecture
- The build script now start the build of all 4 Android architectures (arm, arm64, x86, x86_64)

Problem: build targeting Windows XP is broken

Solution: fix build issues

Revert "Problem: pkg-config file cannot be used for static linking on…

This reverts commit 765c2474.