(__all__): Removed CONT and added BREAK.

(CONT): Removed.
(BREAK): Added.
(controller.__init__): Remove the __done attribute.
(controller.loop): The default is now to continue.  Break only if
	the user explicitly breaks out of the loop.  All references to
	__done removed.
(controller.re): Remove __done accesses.
(controller.eof): Ditto.
(controller.timeout): Ditto.
(controller.cont): Method removed.
(controller.__run_expectations): Default is to continue, unless
	the callback returns BREAK.
(expect_after): A callback should return None or BREAK; not CONT.
(expect): A missing callback is treated as a callback that returns
	BREAK.