Pretty big balance pass, and 1 major bugfix

• Bugfix: Boomer explosions can now actually hurt the player!
• Boomers now do less damage than the max hp of a boomer, preventing mass chain explosions
• Enemy stat ups are now cumulative
  • Previously, enemy stat ups were calculated like: baseStat * (upgrade1, upgrade2, upgrade3, etc)
  • Now, enemy stat ups are calculated like: baseStat * upgrade1 * upgrade2 * upgrade 3
  • Should result in a much steeper difficulty curve over time, and hopefully make infinitely powerup runs less common, if not impossible
• Laser quad beam is now only a tri beam
• Enemies spawn slightly slower
• Starting battery capacity has been increased slightly
• Slight nerf to freezing
  
• Tank upgrades (max hp, reduced damage, etc.) nerfed
• Tweaks to many enemy starting stats

Thanks so much for all the helpful feedback! Keep it coming, and I'll keep balancing/making changes!