We can now reply empty close, ping and pong frames, or close
frames with a payload.
This means that we can send a frame and then close the connection
in a single operation.
If a close packet is sent, the connection is closed immediately,
even if there was frames that remained to be sent. Cowboy will
silently drop any extra frames in the list given as a reply.
In some situations, the underlying socket might become "half-open" in
which case the websocket will stay in a waiting state indefinitely. The
detection of this state requires checking for errors when calling send.
Header names are now binaries. Since header names are case insensitive
they are all converted to lowercase. For example: <<"content-length">>.
The max_line_length option was removed. Three new options have been
added instead:
* max_request_line_length (defaults to 4096)
* max_header_name_length (defaults to 64)
* max_header_value_length (defaults to 4096)
