Crystals - Implemented collision detection
Animation - added `delay`, `savePosition`, and `restorePosition`
Crystals - Implemented collision detection
Animation - Easing - fixed the `swing` animation
Bullets - Fixed JS error
Physics - Collisions - Reversed the collision-detection direction to right-to-left, so that items can be erased from the arrays as they collide
Test - Physics - Added test for collision detection