socket: add portable socket abstraction.
build: bump libbson
socket: various socket work.
stream: various stream socket work.
counters: remove debug code.
build: add tracing option.
socket: get socket stream abstraction working.
trace: update printf macros
build: update symbols for windows.
socket: remove compat layers that are not necessary now.
stream-file: add mongoc_stream_file_t
build: start porting examples to new api.
tests: update mock server to new api.
tests: more api tracking.
tests: more portability fixes.
tests: implement file helpers, just used for tests.
socket: more porting to new socket code.

still some fallout. need to get ssl tests in place.
socket: wait for POLLIN on server socket during accept.
build: add symbols.
build: update symbols for cmake