fixed a bug...  fix in source will be checked in later

what was happening was, the bottommost led would indicate keyboard
startup, but wouldn't turn on after that.  turns out, i had been setting
timer/counter 0 to output on that pin, unnecessarily - because i didn't
understand how to set up timers o_o .  complicated little things.
timers working!

keyboard scanning at almost exactly 200Hz (or maybe exactly... as close
as i can measure)

possible to schedule things to run in 'n' scan cycles!  haven't tested
scheduling things to run in 'n' milliseconds, but the code is so similar
that it should work too.  :D