Update Haystack indexer to use Xapian

sith/settings.py

@@ -184,8 +184,9 @@ TEMPLATES = [
 
 HAYSTACK_CONNECTIONS = {
     "default": {
-        "ENGINE": "haystack.backends.whoosh_backend.WhooshEngine",
-        "PATH": os.path.join(os.path.dirname(__file__), "whoosh_index"),
+        "ENGINE": "xapian_backend.XapianEngine",
+        "PATH": os.path.join(os.path.dirname(__file__), "search_indexes", "xapian"),
+        "INCLUDE_SPELLING": True,
     }
 }