Resolve conflicts
Remove SpriteSheet as it doesn't have any uses
Really use Game.Box and Game.Vector2
Make _.extend more useful
Add more to Tile
Fix errors, bugs, and inconsistency
Be more specific in Game.SpriteManager.add
Add some basic codes and delete unnecessary codes
Merge branch 'dev'

Conflicts:
	css/style.css
	index.html
	js/engine.js
	js/main.js