- Update `create_spp_info_data()` to make data cleaning functionality more
  robust for the BirdLife species' range dataset.
- Update built-in helper script for processing area of habitat data to
  include (i) mammal speices with terrestrial and freshwater distributions and
  (ii)  mammal speices with terrestrial and marine distributions
  (see `inst/scripts/aoh-data.R`)
- New built-in helper script to download all species identifiers from the
   IUCN Red List (see `inst/scripts/iucn-species-list.R`)