Enemy rework

• Replaced old enemies with two new ones: a small & weak one, and a stronger one that enrages periodically
• Updated their movement, they now predict player movement
• They now look better and have basic animations
• Added knockback to their attacks

Visual update

• Placeholder for player
• Projectile & muzzle flash
• Explosion updated
• Other minor updates

Stat tracking

Kills and distance traveled are now tracked and displayed when the game is over