Helpers and Projectiles in 1.1 support an undocumented postype of `none`. With postype set to `none`, the Helper or Projectile will be spawned offset from the stage center.

This postype option was documented for Explods, but was missed in the documentation for Helpers and Projectiles, despite being functional.

This is also the only postype option which breaks this rule from the post: "In all cases, off_y is relative to the position of the player". In the case of `postype = none`, off_y is relative to y = 0 (i.e. the floor of the stage).