Transition table

Added a simple transition table. It's a list of state pairs with a
condition function, and the FSM goes through them after every update.
Decouples states from one another, allowing greater reuse of common
states.

Previous Slime demo done with transition table instead. (line 40)
https://github.com/volvis/HaxeFlixel-FSM/blob/master/table/SlimePink.hx