Redgettext

- fixed one last attribute error left from v3.4 release

- fixed attribute and name errors that were introduced in the previous release

- Added support for detecting call to gettext in f-strings

- fixed `TypeError` when excluded files option wasn't provided
- msgids are no longer incorrectly double-escaped
- fixed encoding of the script

Real date of release: 2020-07-22

- Allow `--excluded-files` to be specified multiple times, thanks retke! (2)

Changes
- Added `--omit-empty` flag to skip writing empty `.pot` files.