ifc2ca, bcf, opencdeserver - add Python 3.9 support

Was breaking due to `|` operator used in annotations instead of `Union`

src/bcf/bcf/inmemory_zipfile.py

@@ -6,6 +6,7 @@ Copyright (c) 2017-2020 Anthon van der Neut, Ruamel bvba
 original idea from https://stackoverflow.com/a/19722365/1307905
 """
 
+from __future__ import annotations
 import zipfile
 from io import BytesIO
 from os import PathLike

src/bcf/bcf/v2/bcfxml.py

@@ -1,5 +1,6 @@
 """BCF XML V2 handler."""
 
+from __future__ import annotations
 import uuid
 import warnings
 import zipfile

src/bcf/bcf/v2/topic.py

@@ -1,5 +1,6 @@
 """BCF XML V2 Topic handler."""
 
+from __future__ import annotations
 import datetime
 import tempfile
 import uuid

src/bcf/bcf/v3/bcfxml.py

@@ -1,5 +1,6 @@
 """BCF XML V3 handlers."""
 
+from __future__ import annotations
 import uuid
 import warnings
 import zipfile

src/bcf/bcf/v3/topic.py

@@ -1,5 +1,6 @@
 """BCF XML V3 Topic handler."""
 
+from __future__ import annotations
 import datetime
 import uuid
 import zipfile