Alternative base layer for Pibow type case with cutout for micro-SD card adapter

This layer has a cutout to clear the extra depth required if you use one of the various micro-SD card adapters available.

I also added some feet to help ventilation, and hide the screw heads.
OpenSCAD file is included if you want to change anything. The file is written in a very basic style, so it should be easy for beginners to work out what each part is doing.

(This is not strictly a remix of the HiFiBerry case, since I did not have the source files. I built this from scratch to