New weapons, effects, optimizations!

Welcome back!

I've got a juicy update this time:

• Weapons and their upgrades have been further refactored to make it easier to add more content
• Added brand new weapon effects like stun and (proper) knockback, weapons can have any combination of effects
• Stunlock weapon was rewritten to make use of new stun and knockback effects, making it pretty OP at the moment
• Throwing knife and other projectiles were refactored to make them much easier to customize and now they use the same damage calculations as melee weapons
• Added on-screen effects when you pick up XP gems, gold coins, and deal damage
• Adjusted the XP curve for character level progression
• Adjusted XP drop-rate from enemies