Accumulator enhancements

[nealkruis]

• Add acmIntegral which multiplies the values by the time durations

• Enhance to handle sources with variability other than subhour. For example, MTR values are hourly. Would be useful to be able to track daily min/max of energy use perhaps. Are there other non-subhour values of interest?

• Consider adding "prior". Current scheme probably has trouble with using last hour's average of something in current hour expression.

• Allow implicit creation of accumulators for specific EXPORTCOL/REPORTCOL where the user just specifies the type of output (Mean, Min, Max, Sum, Integral) and the output is delivered based on the frequency of the parent EXPORT/REPORT.

  EXPORT exFreq = "HOUR"
  EXPORTCOL "Average Zone Temp" colVal=@Zone["Conditioned Zone"].tz colAcm="Mean"
  

  would implicitly create an accumulator with the same value as the colVal and export it as @accumulator[X].H.acmMean