Increase output jack precision using internal temperature ADC

[danngreen]

Some quick measurements shows a correlation between the internal temperature ADC channel and output CV error. temp-adc branch demonstrates this.

A small lookup table with interpolation could compensate.

Also we could have a warning on the calibration page is the temperature changes over the course of calibration.

I did not see any variation of the input CV jack readings of a "cold" unit (just powered on at room temp ~25C) vs. a "warm" unit (been powered on inside a fully enclosed case for >20 minutes)