Improved favicon support;
Added support for stats library;
Improved flexibility of Box#collides;
Removed Collection#overlaps since it was redundant with Box#collides;
Added Collection#collideAll to support checking items in a Collection against each other for collision;
Falling is now supported even when there are no solids;
Changed return value of Actor#collideSolid;
Actor#updateAnimation now takes an optional `collided` parameter;
Improved Sprite caching for flipped images