* Add ZMQ_ROUTER_NOTIFY draft socket option

RELICENSE: Szekely Gyorgy

Problem: unused get_credential methods and associated fields

Migrate and extend probe router test

Solution: remove them

Solution: add receive call for routing id

Code style improvements

Solution: add test case

Solution: migrate to unity/testutil_unity

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Problem: wepoll outdated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