ggstats 0.6.0

Improvements

• new function hex_bw() to identify a suitable font color given a background
  color (#57)
• new default value "auto" for labels_color argument in gglikert() and
  gglikert_stacked() (using hex_bw()) (#57)
• new argument data_fun for gglikert(), gglikert_data() and
  gglikert_stacked() (#60)