Puzzle box with rotating discs

This is inspired by (but not a faithful copy of) Kagen Sound's lovely [Disc Box](https://www.instagram.com/p/ByDad8VHx2l/). The OpenSCAD source and a python script for generating puzzles are included.

Be warned that the python script is very, very slow and may consume lots of memory, because it's not any cleverer than necessary and produces a random box basically by brute force, rejecting puzzles which have serious design flaws like having completely immobile discs (if someone wants to write a better one, I'm for it).

To design a puzzle, run the Python script with the dimensions you like. I wouldn't suggest trying to go above 4×5 unless you have processing power to burn. The script will produce an image of the solved puzzle and tell you how many of each disc type to print (there are 10 different "shapes", which I've given slightly fanciful names to). If you're doing a puzzle other than 2x3, or if you're implementing the --bulge-idlers option, you'll need to change and recompile t