This is confined to pure ASCII, but does support Alt Gr. This is enough
to make a French keyboard layout work:
* home row is "qsdfghjklm"
* numerals are all shifted
* keys like {} require Alt Gr
While not tested, this should also support layouts like Colemak with
the necssary keymap file.
Layouts can be produced from Neradoc's keyboard layout modules on the
device & loaded at runtime. Code to do so is at
https://gist.github.com/jepler/597c0a00e0eb014a433e03c0ae363a08
as well as a sketch of how an extended format could support dead keys &
the full Unicode BMP instead of just ASCII.
