Update v0.3

Update v0.3 is the biggest one yet! Here's what's changed since v0.2.1:

• Updated heart sprite.
• Updated shot spread pickup sprite.
• Updated HUD:
  • Kill count has changed to score.
  • Score is now in the rightmost HUD box.
  • Resized the HUD box for the ammo indicator.
  • Pellet penetration upgrade progress is now shown on the HUD.
  • Pellet count is now shown on  the HUD.
  • Shot spread width upgrade progress is now shown on the HUD.
• Particle effects have been added:
  • Shotgun blast when firing.
  • Splintering wood when pellets hit the fence.
  • Blood splatter when pellets hit zombies.
  • Linear blood splatter when pellets penetrate zombies.
• Fixed a bug here pellets did not penetrate zombies properly.
• Maximum pellet penetration was dropped from 100 to 10.
• Dynamic game balancing has been implemented:
  • Zombie spawn frequency now increases as pellet penetration gets upgraded.
  • Mid-field zombie spawns now appear when shot spread width gets upgraded.
  • The number of zombies per wave now increases with the number of pellets per shot.
• Removed an exploit that allowed slam-fire.
• Overhauled the player movement code:
  • Moving diagonally is now the same speed as moving straight.
• Fixed an issue where zombies would only face diagonally towards the player, never straight towards the player. 
• Slowed down the reload speed.
• Added score multipliers:
  • The multiplier doubles for every five kills per shot.
  • The score is now animated.