Handling higher taxonomic names

[hannahlowens]

Also from @damianooldoni:
"why don't you allow the user to specify the rank itself by adding an argument rank to the function? In this way you make your function much more useful... you can add a default value ("species") to this new argument. This is also important as it can be applied for a multi-species search! You can just pass a vector of species to argument taxon or simply the parent name, e.g. Gadus to get all occurrences of Gadus spp.

I would also suggest to add (at least) a kingdom argument to avoid hemihomony. An alternative would be to allow the user to select which taxon he/she means if GBIF returns multiple taxa instead of choosing the first key.