Added {function} template, #419

tests/template_function.py

@@ -0,0 +1,20 @@
+""" Example showing how to use a custom function for osxphotos {function} template """
+
+import pathlib
+from typing import List, Union
+
+import osxphotos
+
+
+def foo(photo: osxphotos.PhotoInfo, **kwargs) -> Union[List, str]:
+    """ example function for {function} template
+
+    Args:
+        photo: osxphotos.PhotoInfo object
+        **kwargs: not currently used, placeholder to keep functions compatible with possible changes to {function}
+
+    Returns:
+        str or list of str of values that should be substituted for the {function} template
+    """
+
+    return photo.original_filename + "-FOO"