v0.2.2 - Minor changes, art style

Gameplay Changes:

• Ball glows when powerup is picked up. Glow intensity is determined by the duration left of the powerup.
• Tanks now explode when they land upside down
• Health powerup now heals 25% of missing health. (was constant 10% before)

Art Changes:

I initially wanted to go with a silhouette art style as I've got hardly any experience with art design. I changed the background from the checkered to pitch black to how it will go. I'm hoping to get feedback and suggestions about the art style in general.