optimize reading performance

[lesismal]

related:
gorilla/websocket#843

If the pr in gorilla is accepted, we can just add a similar configuration, else we need to change the implementation using NextReader.

[ghost]

The code using NextReader will look something like this:

var buf bytes.Buffer
for {
	t, r, err := s.conn.NextReader()

	if err != nil {
		s.melody.errorHandler(s, err)
		break
	}

	buf.Reset()
	buf.ReadFrom(r)
	message := buf.Bytes()

	switch t {
	case websocket.TextMessage:
		s.melody.messageHandler(s, message)
	case websocket.BinaryMessage:
		s.melody.messageHandlerBinary(s, message)
	}
}

[lesismal]

well, that's good