Game framework with an emphasis on efficient event coordination

Provides basic game logic entities to manage a game where the logic is executed by turns: Game, GameTurn, GameEvent, Turnable. Also offers a bucket system to plan future events at a known number of turns in the future: Bucketable and the services act_next and act_in.

Efficiently support large number of entities with rare or sparse actions, such as a forest with many individual trees growing slowly.