Stepper Shaft Key

This is a remix of the direct drive key by Marty Rice, which he published together with his awesome direct drive extruder (thing #501755).

It's just a tiny bit stronger and uses a tiny bit more material, otherwise it's almost identical, the main difference is I wrote the code from scratch in OpenSCAD, so it can be remixed at will.

WARNING: do not try to turn the stepper shaft with this key while the stepper is enabled!

And also: read the instructions before printing!