get_service_type will return the type of service or layer for the
respective URL (or html) that is passed to the function. For a feature layer
the function should return "feature_layer", for a Image or Map Server the
function will return "image" or "map", respectively.
get_geometry_type will return the geometry type of feature service
layers housed on an ArcGIS REST API server. If a URL is provided that points
to a map or image layer the function will return an error (i.e. only
feature layers have geometry types).
get_supported_operations will simply return a character vector that
lists the supported operations for url.