New Mobs and Other Changes

- Added Healer mob that mainly lays down AoE heals for other mobs, but can also attack the player with a ground spike

- Added a Skeleton Archer that shoots arrows at the player

- Added a crosshairs to more easily see where the mouse cursor is

- Added Game Stats that can be seen when the game is paused (via TAB) or after the game is over

- Shockwave and Gravity Well both now cost only 50 Mana

- Other small bug fixes and adjustments, including statically typing nearly all variables in the code, which should improve performance a bit