The function returns either a single item of class "try-error"
describing the reason for failure (either misdefined parameters or an error
from the Neotoma API), or a table of sites, with rows corresponding to the
number of individual sites returned by the Neotoma API.
Each "site" object contains 6 parameters that can be accessed as well:
siteid, sitename, location, altitude, description,
limited collection units information.