Generate boolean methods which tell whether an event makes sense in current state

[aivarannamaa]

Currently, an event is simply dropped, when raised in a "wrong" state (ie. in a state where it doesn't trigger any outgoing transitions or state reactions).

Some applications would benefit from generated methods which allow querying the state machine whether some event makes sense or not in current state (eg. for disabling some UI buttons or just raising an exception to signal a programmer error)