struct StateTransitor(StateType, EventType, StateType defaultStateParameter = StateType.init, ProcHandler = void delegate()[], ExceptionHandler = void delegate(Exception)[], EventHandler = void delegate(EventType)[], StateChangedHandler = void delegate(StateType newSts, StateType oldSts)[], ConsumeMode consumeMode = ConsumeMode.combined, EventContainer = SList!EventType)
Add event handler
If other handler has already been set, handler will be added to the other handler and executed.