Parametric magazine inserts for UpLula loading tool

This is a customizable insert for UpLula magazine loaders, to precisely fit undersized magazines.

BadFishy's original insert was a good idea, but I thought it needed a few tweaks:

* shortened the overall length, and added a lip to pull it out.

* filleted the corners for easy insertion and removal.

* rotated it onto its back to be printable without support or brims.

* added customizable text to indicate what magazine fits.

* included an OpenSCAD parameters file for all of the STL files I included (M1911, Ruger American 9mm, Ruger LCP Max, Smith & Wesson CSX, Walther PPK/S, Browning HiPower, Star Firestar, CZ-75B). Update: added Glock 22/23.

Note that customizing for your magazines requires [adding the BOSL library](https://github.com/revarbat/BOSL/wiki) to your OpenSCAD install. You may also need to select a different font, if you don't have the free [Noto Sans](https://fonts.google.com/noto/specimen/Noto+Sans) set installed.