This application tries to help finding elecrical shorts in the dev-bridge
board by configuring all pins but one at a time as input (pull-down), and
then outputing a bit to one pin and checking that none of the input pins
go high.

Usage:

Flash it
picocom -b 115200 /dev/ttyUSB0

You should see nothing but line feeds in the terminal emulator.

Red LED should stay OFF.

Blue and green LED should toggle (in tandem).