MPCNC tool mount nut trap

This is the nut trap for the MPCNC (Mostly Printed CNC by Allted) I made using the parametric design by GeoDave. I've completely rewritten the SCAD with a number of improvements, like better code re-use and clearer variable naming.

Additionally, it uses the same measurements Allted describes [in this picture](https://www.v1engineering.com/wp-content/uploads/2015/08/zrail.jpg) on [the MPCNC conduit assembly page](https://www.v1engineering.com/assembly/conduit-rails-tubes-pipes/), whereas GeoDa