ACTUALLY simplify STAT responses.

Fml.
Simplify the state listener.

The state listener is now also a Responder.
Make Player use IfCurrentStateIn exclusively.

This is in preparation for splitting off PlayerState.
Separate PlayerState from Player.

Cue anguished screamings from Charles.
Combine position and state responders.

They'll always be the same thing!
Unify all the response source code.

Woop woop inheritance
Rename io_responder to io_response.

A more generic name for a quite wide-ranging file pair.
Rename Response to ResponseCode.

May need some :lipstick:.
Rename Responder to ResponseSink.

Also clean up some false positives from the previous commit.