roijeric's Printrbot Simple Spool Holder modified for smaller spools

I wrote an OpenSCAD script that cuts up the central part of roijeric's spool holder and moves the corners closer, so it can be used with spools smaller than the original 72mm. The "length" of the spool holder can also be adjusted (might be necessary for spools with smaller radius I guess).

I have included an STL for 40mm spools, slightly shortened to fit a small printer.

The feet are unchanged from the original; I have included the STL files for completeness.