TMK Alpha 28 case

I recently assembled an old PCB I had of [PyroL's Alpha 28 keyboard](https://github.com/PyrooL/Alpha), and needed a case for it.

This case is designed to fit the PCB and Pro Micro controller board (both USB B and C variants) without need for additional standoffs. All you need are some M2.5 heat set inserts and some M2.5 bolts. The top is 3mm thick, so the minimum length of M2.5 screws is 4mm, but use however long is appropriate for your heat set inserts. I used M2.5x6.