sync with latest cowboy code.

Latest cowboy is now using ranch to handle socket connections. This
change reflect it. Also since the cowboy req record is now opaque do a
manual import hoping it won't change often. We could of course use the
cowboy api but it would be came pretty inneficient also it doesn't
expose the buffer.
Use ranch in the readme as well
use master
fix http_req record
whitespaces
use new cowboy_req:get/2, cowboy_req:set/2 methods