A property that can make the projectiles with direction_only = true to travel through an arc, like the particle_vertical_acceleration property of the "stream" prototype.
Reason:
This bug report showed that using "stream" to simulate artillery projectiles is a misuse of the prototype and causing problem that at least 2 projectiles are fired for each shot.
While posila marked that target_type = "position" will be applicable for turrets, I think it is a good chance to request the proper way to visualize artillery projectile by using the actual "projectile" prototype.
