External display for transverter use - one more update

One more update to the firmware and diagram of the external display for transverters. Since there was a little bit of program space left, I added the support for a VFO A/B swap button.

Now you need two N.O. pushbuttons and one DPST switch.

If you don't want the A/B function, leave out the pushbutton but do insert the 10k pull-up resistor. Same for the dual LO, just put a pull-up resistor between pin 12 and 5Vcc if you won't be using a transverter with input into the UHF region.