Moves Apsis::Primitives::SpriteSheet to Apsis::Sprite::Sheet and adds Apsis::World::Scene
Puts responsibility for drawing of sprites in Sprite::Sheet.
Removes move_rate from World::Actor.
Adds Sprite::Animation, removes it from World::Actor
Adds TODO for safety considerations in Actor.
Refactors World::Actor::rules to use an std::string and be const.
Removes World::Actor destructor.
Adds Sprite::Thing