Add sumlevels 252 and 254 to SUMLEV_NAMES

Add sumlevels 252 and 254 to the list of valid sumlevels. This is
related to censusreporter/censusreporter#34 with proper handling
of sumlevels 250, 252, and 254.

census_extractomatic/api.py

@@ -100,8 +100,10 @@
     "160": {"name": "place", "plural": "places", "tiger_table": "place"},
     "170": {"name": "consolidated city", "plural": "consolidated cities", "tiger_table": "concity"},
     "230": {"name": "Alaska native regional corporation", "plural": "Alaska native regional corporations", "tiger_table": "anrc"},
-    "250": {"name": "native area", "plural": "native areas", "tiger_table": "aiannh"},
+    "250": {"name": "native area", "plural": "native areas", "tiger_table": "aiannh250"},
     "251": {"name": "tribal subdivision", "plural": "tribal subdivisions", "tiger_table": "aits"},
+    "252": {"name": "native area (reservation)", "plural": "native areas (reservation)", "tiger_table": "aiannh252"},
+    "254": {"name": "native area (off-trust land)", "plural": "native areas (off-trust land)", "tiger_table": "aiannh254"},
     "256": {"name": "tribal census tract", "plural": "tribal census tracts", "tiger_table": "ttract"},
     "300": {"name": "MSA", "plural": "MSAs", "tiger_table": "metdiv"},
     "310": {"name": "CBSA", "plural": "CBSAs", "tiger_table": "cbsa"},