FSM undo transition

[AlecTroemel]

The right way to do this is to extend FSM like this implementation https://github.com/davidchin/switchhub
1.a history field that tracks actions taken (along with parameters)
2. undoTransition that pops the last item in history, and goes the other way.
3. onundo_EVENT callbacks

this could then be backported to https://github.com/kyleconroy/lua-state-machine

• fsm storing history
• fsm undoTransition function
• undo add
• undo move
  • figure out how to store the "army" state
• undo push
• undo stone removals as a result of "life/death" rule. Need to find a way to store the "removed stones" as a result of an action on the history stack

[AlecTroemel]

this probably depends on #11