Super-Ellipse and Super-Ellipsoid

2020-10-07: Thanks to Carsten Arnholm on the OpenSCAD mailing list, I finally noticed that the superellipsoid version of this had reversed normals, so I have fixed it.

This generates super-ellipses and super-ellipsoids, generated entirely in OpenSCAD. I have seen other super-ellipsoids, but they depended on python code to generate the scad file.
This is based on the formulas found in [Wikipedia](https://en.wikipedia.org/wiki/Superellipsoid)