box-io: lua-sockets history-less import.
Mak accept() and listen() follow luasocket return conventions.
Do not throw exceptions from coeio_connect_addrinfo() if timeout.
Rename box.io to box.socket.
Rename read/write to send/recv to be compatible with luasocket.
Inline bio_socket_close().
Don't allow connect/bind on a non-empty socket:this is error-prone.
Don't allow connect/bind on a socket which
is already connected/bound/used for something else.
This is error-prone.
Move bind_addrinfo to evio layer.
Don't create iobuf without need. In close(), set iobuf to NULL.
Timeouts are not exceptions. Merge _timeout and other calls in coio.