Added more enemies

There are now more different enemies to fight, including two end-of-level bosses. After defeating a boss, you go to the "next" floor, which for now is just a random reroll of the first floor again. Bosses are balanced around the expectation that you'll be using spells on them, not just normal attacks.

Other changes include a major change to the way shop prices and enemy treasure drops work, and several smaller gameplay adjustments.

Note that the lives system still does not work, and the game will freeze the first time you run out of health instead of giving you a chance to respawn.