Unix sockets and Windows hammer test

Ability to import / export FDs to/from socket contexts for use with uWS::LocalCluster
Fixes the case of receiving a full receive buffer followed by an immediate socket hangup

@oksdav

What's Changed

Fixes for FreeBSD by @oksdav in #205
add us_socket_remote_port(int ssl, struct us_socket_t *s) by @Jacob-Burckhardt in #210

Full Changelog: v0.8.6...v0.8.7

Adds us_socket_write2

uSockets should never be built as DLL; it should always be built as a static library (and if available, LTO).

Being an opaque low level library means dynamic dispatching of low level calls such as us_socket_ext entirely ruins performance.

The library should always be built as a static library

CI now builds and runs hammer_test on Windows as well, covering all three platforms.
Unix sockets.
Experimental UDP sockets.

Never pass invalid send flags to Linux

Includes changes mentioned in v19.4.0 and v19.5.0 of uWebSockets.

Applies a patch, fixing a "deadlock" where SSL_read fails to perform the initial handshake because of send failing with too much backpressure - causing the SSL socket to remain stuck in "limbo" mode until it times out. This fix gracefully handles this edge case.