so you've got a full screen sketch, but that means you're gonna hide the
stop button.. but then you've gotta write an exit handler.. how to warn
people about this or enforce a default "exit" when running in present mode?

(problem with default exit, of course is that sometime people will want to
shut that off too.. yay! complexity!)

nevermind... just use ESC to exit, or if people override ESC, they can deal
with it themselves.