YOU WILL NOT SURVIVE PAST WAVE 3

- Optimized collisions (untested, lmk how that goes)

- Added an unpause button so you don't need to press esc

Added a "YOU WILL NOT SURVIVE PAST WAVE 3" mechanic for beginning players where YOU WILL NOT SURVIVE PAST WAVE 3. This was done for a couple reasons but mainly -- the first run tends to be pretty bland cuz you can get pretty far with just the ballista. Instead of just rebalancing the game like any normal person, I'm cutting off the run early and encouraging the player to buy upgrades.