Columpius - smooth algebraic surface

Columpius, a smooth algebraic surface of degree four. This is the set of real points for which
```
x^3*y+x*z^3+y^3*z+z^3+7*z^2+5*z = 0.
```

Has two holes!

I have provided these files:
* `columpius_smooth_thickened.stl` -- has the normal vectors fixed, and is thickened for printing. I should re-do this one, because there are artificial self-intersections near one of the holes. I now know how to do this step better.
* `Columpius_Blocky_Xy_thickened.stl` -- the blocky version, good for printing
* `columpius_raw_blocky_xy.stl` -- raw triangulation coming from Bertini_real. Since the program works in arbitrary dimensions, I make no effort to control normals from it -- they don't exist for 4- and higher-dimensional surfaces, but instead a tangent space which is not immediately useful for 3d printing. Hence, the surface was thickened in Blender, before being passed through Microsoft's 3D Builder to fix internal geometry. The raw versions are not directly suitable for 3d pri