Design a "direct GPIO to XLR" board

[kripton]

See jostlowe/Pico-DMX#27 and https://github.com/kripton/rp2040-dongle/tree/DirectDifferentialOutput: It's possible to directly control fixtures via the GPIOs, not necessarily do we need an RS485 driver. While one cannot drive 16 universes that way (not even 8), it might allow for a very cheap IO board