- Prevent generation_date tag format from being modified when SAVE_DATE_FORMAT is
specified
- Prevent NoneType from ending up in the tags (previous fix did not work)
- Update DATE_FORMAT to be configurable using the SAVE_DATE_FORMAT environment variable
- Modify target filename generation to handle cases where SAVE_DATE_FORMAT is left blank
- Default to date format "%Y-%m-%d" if SAVE_DATE_FORMAT is not set