turning stratumStructure into an s3 generic.
Merging github origin/master back in to the stratstruct branch.
The s3 generic stratumStructure() now passes eisting tests.
effectiveSampleSize is now generic, enabling us to avoid computing twice within stratumStructure.default the same table of treatment and control counts by stratum.
removing unnecessary ... arguments, making effSamSize.optmatch a factor method instead