Changes to unbox the state in the ST and IO monads.

ST now has type

	newtype ST s a = ST (State# s -> STret s a)
	data STret s a = STret (State# s) a

IO now has type

	newtype IO a = IO (State# RealWorld -> IOResult a)
	data IOResult a = IOok   (State# RealWorld) a
	                | IOfail (State# RealWorld) IOError

So ST should be slightly more efficient, and IO should be nearly as
efficient as ST.