OpenSCAD Customizable Knob

This is a generic customizable knob with a lot of options (and not a lot of error checking so don't change too much at once). Multiple types of shafts can be accommodated including: circle, circle with internal or external keyway, D (partial circle), and any polygon (triangle, square, etc.). There is a test option to generate a simple disc with the specified hole/shaft pattern and mark angle for test fitting prior to printing the full model. The "standard" stl is based on a knob for an old h