This change stores the digi pot indices in the scale 1-255
(previously 1 -128) so the stored values for calibration
are no longer valid after this change is uploaded to Arduino.
Please re-run the full calibration on your Afterburner!
Added support and autodetection of MCP4151 digital pot.
If MCP4151 is detected then its wiper resolution is halved
to match the MCP4131 wiper resolution.
MCP4151-103 is now a drop in replacement for MCP4131-103.
New features:
* unified socket for 20 pin and 24 devices (including GAL20V8)
* variable VPP via digi pot
* VPP measurement via A0 ADC (used for VPP calibration)