Framework 13 vertical stand

The Framework laptop 13 can open up 180 degrees, which made this very simple design possible to create a completely vertical stand.

The advantages of this approach:
- The laptop takes up very little space in this position, making it much more comfortable to use an external keyboard with it.
- The screen is at a great height, the top edge of the display is much closer to where a big monitor of a desktop workstation would be.
- The two pieces of the stand are pretty flat and therefore portable. I don't think twice about throwing this in my backpack.

Notes about the implementation:
- I iterated a few times on the cutouts for the laptop, now they're a perfectly snug fit.
- I was probably too conservative with the dimensions. I think one could make the pieces thinner and all around smaller and still get a perfectly stable setup.

The OpenSCAD source is [here](https://git.buenzli.dev/remo/three-d-models/src/branch/main/src/laptop_stand.scad). (public domain, [Unlicense](https://unlicense.o