#5 Change reactions to have a hierarchical preference setting

[Richard Townsend]

The current reaction grid (Friend/Foe) works fairly well, but ignores the need to react to Hazards. Try a rewrite that uses two levels of priorities: one for element type, the other for the actions.

Default for first priority should be Enemy, Friend, Food, Hazard, Mouse. Defaults for second priority can be (respectively): Forward, FollowFriend, FollowFood, Left, FollowMouse.