Turbine/Impeller for Shark 18v Cordless

Added a toroidal radial taper to the design, so that it would fit our little hand-held vacuum. Basically, it's taller in the middle than on the edges.

The scad is configured to print part of a hand-held vacuum, replacing an injection-molded part that blew apart under use. Also added variables to make the center hollow, which seems to improve suction, and of course sized it up for the vac in question, a Shark 18v Cordless.