#40 New tag for specifing message reciever

[Matt Paulin]

Ok, so there's this other issue I had forgotten about.
Some client messages may tell the server to send
messages to clients other than the sending client.
These server messages aren't technically "responses",
so I suppose they aren't an expected response. But they
will only be generated in response to these client
messages, so it seems like we should explicitly
document that expected behavior.

Maybe make a new tag, similar to expectedresponse, but
instead called something like "generates". Or, per my
previous email, maybe these should be set based, so a
message might generate foo and bar, or baz.

It would be nice to say who the generated messages will
go to, but I can't think of a useful way to do that,
short of a text field. Which, come to think of it,
might be useful enough.