In particular the `pi_revision` thing in PiGPIOPin, all the stuff @lurch
picked up in `pins/data.py` (thank goodness *someone's* watching!), and
make all those links pointing to "Notes" point somewhere useful like
"Pin Numbering"...
Tweak the second keyboard robot recipe so it detects keyboards and
doesn't throw exceptions on unknown keys. Also add a note to the recipe
that it won't work over remote connections like SSH.
