LudvigOlsen/groupdata2: groupdata2 1.5.0

Breaking: Rewrites large parts of the numerical balancing engine used in fold() and partition(). This produces different groups in some cases. Outsources extreme pairing to rearrr::pair_extremes(). Now uses hierarchical shuffling (rearrr::shuffle_hierarchy()) in partition() and some cases of fold() (relevant when extreme_pairing_levels > 1). If you need reproducibility, the last version prior to this breaking change can be installed with devtools::install_github("ludvigolsen/groupdata2@v1.4.2").

Imports rearrr for use in numerical balancing.

Minor improvements to vignettes.