A map of sprites for all 4 directions of the entity, or one Types/Sprite that is used for all directions.
Optional. If omitted and neither #sheets or #sheet are present, the game will not look for any other directions and instead try to load the whole definition as one Types/Sprite and apply it to all directions.
Type: Array of Types/SpriteNWaySheet
Optional. If given, this is used instead of any other properties that may be present.
Optional. If given, and #sheets isnt present, this is used instead of any other properties that may be present.