50g Mini Spool Remix

This is a quick remix of [johannesbehr's design.](https://www.thingiverse.com/thing:129173)
I mostly reproduced the geometry of his design in OpenSCAD so that I could adjust some dimensions and clearances slightly. The walls weren't thick enough for my taste/printer.
*Changes 5/24*
I've replaced the "Case" piece with the simpler "Guard". The Guard modification idea came from another [remix](https://www.thingiverse.com/thing:998090).

This holds 50g filament like often comes in sample packs/multi-packs.

The spool itself now has a 1.0 mm thickness. The case/holder is at 1.0 mm also.

As printed, mine weigh about 22 g (with "cover", or 16 g with new "guard"*). Print it, assemble it, weigh it, and mark it! Then wind those remnants or samples for convenient use.

Spool.stl contains all three parts (Spool A, Spool B, and Guard) ready to print on the bed at once if your bed is large enough.

To customize it, I recommend getting the latest version of OpenSCAD and adjust the param