OpenSCAD Library: Pipe knees (aka maccaroni maker)

Should be obsoleted by my torus rewrite at https://www.thingiverse.com/thing:6764999


Another addition to the OpenSCAD library, for generating bent pipes and maccaroni-like structures. You may want to pull modules pie and torus from this file and write them to their own library files.

Source file has still code of older pie routine, which can now be replaced against the more efficient implementation https://www.thingiverse.com/thing:6754617 - I'll eventually upload an update of this file.