Update 1.2.4

Minimum save file version is now 1.2.4
Fixed: Audio plays at slightly different speeds on different computers.
Fixed: Charm bar incorrectly displays guaranteed charm when it is merely very likely.
Balance: Adjusted the formula used to calculate how much XP is required to level up so that monsters with higher power tend to require more XP to level up.
Backend: Upgraded pygame from 2.1.2 to 2.1.3.dev8
Backend: Upgraded tcod from 13.1.0 to 15.0.0
Backend: Upgrade numpy from 1.21.4 to 1.21.6