Code style improvements

Fixed naming for filter parameter, removed unnecessary temporary variable, fixed naming of local variable

Problem: stream_engine_t instance may access its fields after it deleted itself

Added some more clang-tidy rule exclusions

Solution: prevent access to data if the object was deleted

Code style improvements

Some code style improvements: removed redundant parentheses, added const, joined declaration and assignment of local variables

Use static_cast instead of C-style casts, make local variables const where possible, use switch instead of chained if/else, extract rm_helper_multiple_subnodes from rm_helper to reduce nesting

Problem: wepoll outdated

Simplified and optimized several code fragments

Solution: update to wepoll 1.5.2

* Problem: No CI for mingw64

Adding CI support for mingw64 to appveyor.yml

Reason: To help address the issue:
  Several checks fail under 64-bit MinGW on Windows when running make check #3185

* Problem: Docs do not build with mingw64, dll already in right place

Turning off WITH_DOC for mingw64
Removing copy command for mingw64 and cygwin64 (it now seems to be directly built in "bin" directoy)

Problems: no docs for zmq_timers_*, zmq_timers_* have been DRAFT for a long time

Solution: move them from DRAFT state to STABLE

Solution: add it to the makefile

Solution: add a manpage
Fixes #3005

Race condition with received message causes ZMQ_CONNECT_ROUTING_ID to be assigned to wrong socket

Solution: Add an identifier parameter for local attach to zmq::socket_base_t::attach_pipe

Problem: build system does not play nicely as a cmake subproject

Solution: avoid exporting targets and installing files if neither
BUILD_SHARED nor BUILD_STATIC is set

cmake: Install pkgconfig in correct lib directory.

Solution: Use cmake's libdir variable to ensure that the pkgconfig file
ends up in the correct lib/lib64 directory. This matches the autotools
behaviour.