This application uses `soft_uart` to bit-bang the name of a number of
configured GPIO pins via said pins at 9600 Bd. This way attaching an
USB UART bridge to one pin at a time easily reveals which MCU GPIO
pin a given pin on a board corresponds to. This is useful when no
schematic and no silkscreen labeling is available, or when the
information is misleading or outright incorrect (looking at the
E180-ZG120B-TB).
