todo.todo

Basic Game Checklist:
- [X] Create a player (Player)
- [X] Shoot projectiles (Projectile)
- [X] Create enemies (Enemy)
- [X] Detect collision on enemy / projectile hit (Animation loop)
- [X] Detect collision on enemy / player hit
(cancelAnimationFrame)
- [X] Remove off screen projectiles (we still calculating for the off screen projectiles, and to improve performance, we need to remove them)
- [X] Colorize game
- [X] Shrink enemies on hit
- [X] Create particle explosion on hit
- [X] Add score
- [X] Add start game button
- [X] Add game over UI
- [X] Add restart button
- [X] More accurate object removal (when using splice, loop from the back of the array)
  - When we remove an object from an array using splice, the items after removed object will shift one place forward
  - If we iterate from the beginning to the end, we might skip the particle next to the removed object.
  - But if we iterate from the end to the beginning, this problem can be solved. 
- [ ] Add background music
- [ ] Add sound effects
  - [ ] When player shoots the particle
  - [ ] When enemy gets hit by the particle
  - [ ] When enemy dies
- [ ] Resize event