Bow Attack + Weapon Swap

[mnmaita]

Fixes #137

• Added PlayerWeapon plugin that manages swapping between the Sword and the Bow weapons.
• Added a new keybind (H key) that swaps weapons for the Player.
• While using the Bow weapon, the Player now shoots arrows when pressing the attack key.
• Added configurable velocity variable for the arrows shot by the Player.
• FIxed a few typos in comments.

[mnmaita]

TODOs:

• Despawn arrows when they hit walls.
• Remove gravity from arrows? Although right now with a high velocity value it's working great even for hitting several enemies in a straight line if that gets added as a passive later and it looks cool visually.
• "Auto-aim" feature.