Problem: duplicated socket_poller::wait() code

zmq::socket_poller_t::wait() had an important set of common lines
between POLL and SELECT variant.

Solution: refactor zmq::socket_poller_t::wait() and add the
following methods:

zmq::socket_poller_t::zero_trail_events()
zmq::socket_poller_t::check_events()
zmq::socket_poller_t::adjust_timeout()
Signed-off-by: Marc Sune <mardevel@gmail.com>

Revert "Problem: term "identity" is confusing"

Problem: term "identity" is confusing

Solution: use "routing_id" instead

Solution: Replaced by "routing id"

Solution: change docs to refer to "Routing id"

Solution: Renamed, but support querying the property by its old name

Solution: Replaced by "routing_id"

Solution: renamed routing_id fields in pipe_t, renamed ZMQ_CONNECT_RID to ZMQ_CONNECT_ROUTING_ID

Solution: replace by "routing id"

Problems: typos in proxy_steerable stats

Solution: fix it

Solution: fix it

Problem: proxy_steerable STATISTICS returns conflated buffers

Solution: split each stat into its own frame, to make it simpler and
easier to use it, especially from high level bindings

Problems: proxy stats test break 32bit build, not declared as draft

Solution: ifdef it until it's declared stable

Solution: trucate 64 bit stats in test_proxy, as it's much easier than
to try and print 64 unsigned integers in a portable way

* Issue #2736: Add STATISTICS command to zmq_proxy_steerable()

Variable is assigned but is not used until the end of the function

Excessive check options.mechanism == ZMQ_NULL

The '||' operator is surrounded by opposite expressions. session_base.cpp 377

Problems: compiler warnings

Solution: add /* FALLTHROUGH */ comments so that nagging compilers
don't nag

Solution: wrap arguments with LIBZMQ_UNUSED

Solution: don't pass it

Problem: assertion in src\select.cpp:111 on Windows or hang on zmq_ctx_destroy

Problem: unable to query state of a router for a particular peer

Solution: added function to zmq_draft.h

Solution: added tests

Solution: use inproc transport instead

Solution: refactoring

Solution: modify order of operations, add diagnostic output

Solution: add initial implementation

Solution: added call

Solution: extract as_socket_base_t function

Solution: added test case (with dummy implementation of zmq_socket_get_peer_state)