add args to Transition

[okhowang]

related #16

[qmuntal]

Can you specify why you need the arguments in the Transition? They are normally already passed in the function call-backs.

[okhowang]

I want write log once state changed for debugging state machine. And args is the detail info of transition.

[qmuntal]

I'm hesitant to add the Arguments property to Transition. It does make sense but there are already many callbacks whose parameters are a transition and the arguments, so it would be confusing to have the arguments in both place.

Yet your use case is valid, so I will think on a way to cover it. Other proposals are also welcomed.

[okhowang]

@qmuntal is any better way here?