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.