The default_geocoder() will return the ArcGIS World Geocoder if no
token is available. list_geocoder() requires an authorization
token.
The ArcGIS World Geocoder
is made publicly available for some uses. The world_geocoder() is used
as the default GeocodeServer object in default_geocoder() when no
authorization token is found. The find_address_candidates(),
reverse_geocode(), and suggest_places() can be used without an
authorization token. The geocode_addresses() funciton requires an
authorization token to be used for batch geocoding.
To manually create a GeocodeServer object, see geocode_server().