End-Game Screen + Bugfixes!

Added a new endgame credits sequence that tells you some stats on your run, so you can more easily take screenshots to boast about your run!  The screen will also tell you if you managed to complete the run with either no lives lost, or no retires, as well.

In addition, there have been a number of small fixes and tweaks:

• Fixed bug where upgraded Bomb towers would sometimes shoot the end of the maze instead of the start
• Optimized performance of all projectile-shooting towers
• Fixed bugs caused by optimizing performance of all projectile-shooting towers
• Starting a new game now prompts you before erasing things
• Fixed bug where enemies would sometimes not generate particles upon death
• Fixed bug where water tower would incorrectly cancel a shot if target enemy died
• Fixed bug where multiple crossbow towers would attack a single enemy where only one shot was required to kill it
• Fixed bug where final phase of final boss was not correctly affected by difficulty setting
• Fixed small sorting issues on certain enemies