Update - v4

Update v4 is here!

What has changed:

• added new sounds,
• improved revolver effects,
• added the mute audio button to the title screen,
• increased powerup spawn chance,
• decreased dynamite spawn chance,
  
• added new info to tutorial screen,
• life totems are now displayed as images instead of text,
• added crate destroyed effect,
  
• added an indicator showing how much ammo has left in revolver,
• tutorial screen can now be opened from the pause menu,
• fixed bug with train wheels not rotating properly