Adding turn system to game

The state of the player's turn is regulated by the Play object, and flow is
controlled by callbacks to Play. The order is [player input] -> [sprite move] ->
[draw encounter] -> [execute encounter results] -> [wait for player input].
Move variables to ship

"stamina" and "treasure" variables are now attached to ship object. Some other
clean-up work.
Hooked Up Encounters

Encounters now hooked up with the turn structure
Merge branch 'master' into cyphers/implement_turns
Merge branch 'cyphers/implement_turns'