CommandAdapter fails to handle multiple requests in one message

If requests are sent quickly by a client, a single read by the server can contain multiple requests, e.g. `b'N02=0\r\nN03=0\r\nN04=0\r\n'`

If `CommandAdapter` was updated to take a terminator (`\r\n`) instead of a format string (`%b\r\n`), `TcpIo` could handle multiple requests by splitting the data from the read by the terminator and passing each one separately to the handler, but this will break a lot of things. I couldn't see a sensible way to do it with just the format string because it would have to make too many assumptions.