add error ranges comptued from ranges of dms to output sheets

[mef51]

Currently you need to do your burst exclusions and find fits by DM and then call

source = driftlaw.sloperanges(source) # compute drift ranges after burst exclusions

or

source = limitedDMsloperanges(fitdf, source)

See driftlaw.bakeMeasurements for an example, or the first cell of the PaperFigures.ipynb notebook for an example.