Make `classifications` function

[zachary-foster]

This would be an abstraction of id_classifications and name_classifications, that allow constructing classifications from anything in all_names()

 ex_taxmap$name_classifications()
                                          1                                           2                                           3 
                                 "Mammalia"                                   "Plantae"                          "Mammalia;Felidae" 
                                          4                                           5                                           6 
                    "Mammalia;Notoryctidae"                        "Mammalia;Hominidae"                        "Plantae;Solanaceae" 
                                          7                                           8                                           9 
                "Mammalia;Felidae;Panthera"                    "Mammalia;Felidae;Felis"          "Mammalia;Notoryctidae;Notoryctes" 
                                         10                                          11                                          12 
                  "Mammalia;Hominidae;homo"                "Plantae;Solanaceae;Solanum"          "Mammalia;Felidae;Panthera;tigris" 
                                         13                                          14                                          15 
             "Mammalia;Felidae;Felis;catus" "Mammalia;Notoryctidae;Notoryctes;typhlops"           "Mammalia;Hominidae;homo;sapiens" 
                                         16                                          17 
  "Plantae;Solanaceae;Solanum;lycopersicum"      "Plantae;Solanaceae;Solanum;tuberosum" 

would be the same as:

ex_taxmap$classifications(value = "taxon_names")