labelled 2.16.1

Bug fix

• value_labels() works on empty vector, i.e. a logical vector containing
  only NA values (#192)
• dictionary_to_value_labels() now handles value labels with repeated
  delim_value_label (#194)
• fix in set_value_labels() when .overwrite = FALSE (#198, @ LeonidasZhak)
• fix in update_labelled.labelled() when importing na_range attribute
  (#198, @LeonidasZhak)