Changes

• The terms argument can now include up to five focal terms (formerly: four).
  Accordingly, the plot() method was revised. For four focal terms, a facet
  grid is used to plot all relevant panels. For five focal terms, multiple
  plots with facet grids are arranged using the patchwork package.

• values_at() gains a new "threenum" option.

• The test argument is test_predictions() can now also be a formula to
  calculate consecutive contrasts, contrasts against the reference level or
  against the "average" factor level.