MarchingCubes for OpenSCAD function literals

// MarchingCubes for OpenSCAD function literals v0.1 - Torleif Ceder 2020
// With function literals of bounded closed isosufaces in the form f([x,y,z])
// Signed distans function can be output as polyhedron.
// Quality and problens is as expected with MarchingCubes

https://github.com/TLC123/OpenSCAD_stuff/blob/master/MarchingCubes.scad
https://openscadsnippetpad.blogspot.com/2020/12/marching-cubes-for-openscad-function.html