Adds a cannon turret that uses cannon shells.

I have added settings for attack speed, range, damage, minimum range, directional fire, or 360 so you can adjust them to your liking.

Things I've fixed
- Adjusted shot starting far away from the cannon muzzle.
- Removed the extra damage research. I think the default physical projectile damage research is good enough.
- Adjusted particle effects.

Thanks to Touhma for updating this old mod and inspiring me to make my own flavor of it.