* fix/docs: fix mio types we use

* test/udp_rendezvous_server: add integration test;
  also exposed UdpRendezvousClient (not as a crate API though,
  only for internal modules for testing).

* make UdpRendezvousServer return it's listen address (in case
  someone specifies port 0 for it)

* fixed UdpRendezvousServer on Windows where the client tried to
  connect with the server using 0.0.0.0 IP address.

* fix/ci: skip rustfmt on Windows

We hit the rustfmt bug: rust-lang/rustfmt#1873 .
Currently, rustfmt fails to format when path attribute has relative
paths.

Usually, our code does not have too much windows specific code and in
this case there's no such code at the moment. So, it's the easiest fix
is to disable rustfmt on Windows for now hoping for the fix in the future.