hvtiPlotR 2.8.20

• New hv_group_palette(levels): the house colors for the groups compared in
  an outcome figure, named by group. One group is black; two to five take Paul
  Tol's vibrant palette led by red #CC3311 and blue #0077BB, then teal,
  magenta and cyan; six or seven switch to the muted overflow; more is an error
  of class hv_group_palette_capacity. Red and blue now mean the event and
  censored only in figures that draw those roles (hv_role_palette()); in an
  outcome curve they are the two groups that stay most distinct for a
  colorblind reader.