Convert Keyboard docs.

Should `KeyCode` be abstracted out? There's the pitfall of using `toCode 'c'` instead of `toCode 'C'`. Then there's the ability to, with a bit more work, figure out if shift and/or caps lock are down and return that a capital letter was pressed, which ought to make text entry easier. But I suppose it makes localization difficult.

Anyway, this is another straightforward conversion.