coverageContourPlot supports passing WeightedData as data.
loadPlanckChain returns a WeightedData object
Rework loadPlanckChain to loop over all available files and use separate
model,dataset,PLA parameters to build paths.
Add support for selecting arbitrary x,y columns from a larger 2D
dataset in coverageContourPlot.
(Re)implement maxRows option, which was being ignored when reading
multiple files in a chain.
Add some debugging printout to track down possible mathematica bug.