popbayes 1.1

• Change stat_method category G by X (eXpert knowledge) to avoid confusion
  with the category G (Ground counts) in the field_method variable
• Set arguments pref_field_method, field_method, conversion_A2G, and rmax
  to NULL by default in format_data()
• Allow NA values in column field_method if stat_method = "X"
• Function format_data() now works at the count series level (not the whole
  data set). This allow users to define different values for these arguments for
  different counts series (with the same species)
• Function format_data() returns an error if some confident interval bounds
  are strictly equal