Add Software Trimpots about diy-flow-bench

[DeeEmm]

It should be noted that we can already view raw sensor voltage data via the API.

[DeeEmm]

For the moment I've added some definitions to the config file...

#define PREF_TRIMPOT 0.0

etc...

[DeeEmm]

Added trimpots to all input data streams within sensors class.

For example...

double mafMillivolts = (mafFlowRaw * (_hardware.getSupplyMillivolts() / 4095.0)) * 1000;
mafMillivolts += MAF_TRIMPOT;
return mafMillivolts;

Trimpot value can be determined by comparing measured sensor output voltage and calculated voltage in API. The trimport should be set to the difference to bring the calculated value in-line.

This procedure will form part of initial calibration when setting up the shield.

I may revisit this at a later stage to refine how we do this but for a one-off routine I think it is acceptable.