4 char idioms - stereographic projection

As I said in [Stereographic projection maze](https://www.thingiverse.com/thing:2013536), I hit upon a great idea one day. If we waive the maze algorithm aside, there exists an easy way to perform a stereographic projection in OpenSCAD.

I wrote a `stereographic_projection` which can perform stereographic projection on 2D objects. The customizer here is just a demonstration. If `stereographic_projection` interests you, you may find it in "chinese_4_char_idioms.scad". The `stereographic_project