Filter entities by name when extracting data from Arkindex

Closes #134 (closed)

dan/datasets/extract/__init__.py

@@ -85,6 +85,11 @@ def add_extract_parser(subcommands) -> None:
     parser.add_argument(
         "--load-entities", action="store_true", help="Extract text with their entities."
     )
+    parser.add_argument(
+        "--allow-unknown-entities",
+        action="store_true",
+        help="Ignore entities that do not appear in the list of tokens.",
+    )
     parser.add_argument(
         "--tokens",
         type=pathlib.Path,