Added function to collapse to the most detailed common set of intervals
Integrated function into agg and scale along with new argument collapse_interval_cols so that there is an option to collapse the interval id variables that aren't being aggregated or scaled
Add regexp argument to testthat::expect_error calls so that exact error is tested
Addresses #13
aggandscalealong with new argumentcollapse_interval_colsso that there is an option to collapse the interval id variables that aren't being aggregated or scaledregexpargument totestthat::expect_errorcalls so that exact error is tested