ResponseHandlers need a better method of responding to frames which they don't intend to act on

[LeonardMH]

Currently, implementers of ResponseHandler must respond either with None (which results in no response being sent) or a bytes object ready for transmission. This poses a problem with responders when they receive data that they have no intention of acting on.

The current best practice is to just respond with the same data that we received, but that is non-ideal for a lot of reasons.

A simple solution would be to implement a client-response message type which simply acknowledges that the message was received. The server would not be expected to act on that response.

[LeonardMH]

I have 'by convention' been generating a response that just contains:

{
   "type": "ACK"
}

And this seems to work well, because the server just sees this, says 'not a frame' and moves on, so when the socket server is expecting a response this is a nice short way to indicate you got the message but don't intend to act on it yet.

Probably just need to do a bit more testing with this and then document it (or look into whether I need to officially do anything).