Truncated Toroid OpenSCAD base shape

This is a "cheese wheel style" base shape for use in other OpenSCAD designs. It is not directly useful as a part!

The design can be configured to be hollow or solid, and all measures can be adapted with parameters. Might be useful to create barrels, baseball shapes, actual cheese wheels, hollow spheres or to cut to a shape where you need different vertical and horizontal bending radii. Notably, the shape uses `rotate_extrude()` rather than `difference()` for hollow designs, which gives a much better preview performance in OpenSCAD.