v0.3 - AI and upgrades

- v0.3: Added a new weapon, upgrade and adjustments to enemy AI.

• Added Speed upgrade
• Added Hammer weapon
• Enemies of the same kind now try to avoid each other somewhat
• Fixed Archer AI and attack speed bugs
• The Hole in the arena now opens and damages the player and enemies when it spawns new enemies
• Minotaur's drop less coins
• Made Minotaur hitbox smaller