Syringe gun - now 80% more gun! Fixes #1935

Syringe gun uses gun code now. Because guns must be guns, not tons of shitty hacky code. This solves all syringe gun's targeting issues (#1935), it works just like any other gun now. Rapid Syringe Gun buffed to 6 syringes because using a rotating revolver-like cylinder only for 4 syringes is pointless.

No path or vars changes, no map or RnD updates needed, syringe projectile was added by me in #1318.

Fixes #1935