[GreenKeys] USB to TTY-loop possibility...

[epvgk at limpoc.com]

looks like this is working more or less okay, so I'll probably put up at least
a first draft of the firmware over the weekend. The board I'm using is the
"Teensy 2.0" from PJRC.com, but it would work ok on most anything with a USB
capable 8 bit AVR. I'm connecting it to the tty loop using a 6N139 for receive
and a Clare LCA110 for transmit, just because that was what was in the parts
box. pretty fun!