0.33 Release

A boring update:

• Almost all the bullets in the game were moved to use raycasts instead of being full rigidbody physics objects. I made this to improve performance but it ended up not mattering that much. Bullets are able to hit their targets a bit better now though!
• All bullets and most effects now use object pool. This resulted in frames being a lot more stable as no more massive frame dips when many guns happen to shoot at the same time.
• Prologue is now more bug free. It now teaches how to use gems, and have some text to help with understanding.
• Instead of repair drones holding new carts and such, now the train engine holds them. Although it was definitely cool for the repair drone to hold the carts, the mechanic was confusing to new users and it was a bit clunky to use in practice. Losing gems and such by dropping them accidentally was funny but not terribly fun. But I might always bring it back later. Also there is the new problem of having too much "inventory" space by carrying things with the engine (like potato gems). definitely need to fix that somehow.
• Flamethrowers now target the farthest enemy to apply fire to most enemies possible. I'll still do a fire rework eventually but it still works in the meantime.
• Explosive gem now makes the repair cart repair nearby burns too, and makes ammo cart explosion resistant (keeps ammo when destroyed).
• I was getting bored with testing the game so I added difficulty settings to make it harder.