Commit my Atreus case design.
Fix a broken link.
The current layout does have a tab key.
One can get single keycaps from Signature Plastics.
Specify the kind of the mini USB cable needed.

Also: point out that thick USB cable connectors are trouble.
Add tables with row-to-pin and column-to-pin maps.
Check spelling; rephrase description of the wiring of thumb keys.
Fix image links. Replace the thumb key wiring diagram.
Merge branch 'tweaking-readme'
Merge branch 'new-thumb-diagram'
Merge branch 'case'