Raspberry Pi4 case for Prusa MK3

Put a Raspberry Pi4B on your Prusa Mk3S and have it align perfectly with the frame.

- Smallest form factor possible for a Pi4.
- Space for an optional Pimoroni Fan Shim.
- All peripheral ports accessible (not the Pi headers).
- Break away window for Pi-cam - added STL-version without window.
- Windows for status lights.
- Slim attachment block to frame.
- Uses styling cues from the Einsy Case with chamfered corners and textured sides
- Easy to print: no supports needed.

Edit: added a new version of the top part (PiCase-top-compact.stl) which is more compact to allow this to fit with https://www.thingiverse.com/thing:3284730

Uses:
- 4 M3x16 for the case
- 2 M3x10 for attaching to printer

A complete redesign inspired by the Prusa Einsy Case and:
- https://www.thingiverse.com/thing:2334119
- https://www.thingiverse.com/thing:3723561
- https://www.thingiverse.com/thing:3004038