* feat(args): parse `countdown` by time
* fix lint
No `Default` for `AppTime` needed...
* app: pass `countdown_until` down
* fix `parse_duration_by_time` and `parse_duration`
to handle different formats they support
* fix(countdown): percentage panics
`Duration::ZERO` needs to be considered
* `DirectedDuration`
* fix comment
* rename arg: `countdown-target`
* `ss`->`mm`, fix formats, update README
* alias `--ct`
- Extract local state of `app_time_format` from `footer` to have it globally available
- Add a deserialization fallback for deprecated `AppTimeFormat::Hidden`
- Persist `footer_app_time` toggle state
- Add `--menu` to args
- Add `--version` to args
- Change default behavior: At a first run of the app, the menu will be shown by default (similar to what @tschinz suggested in #33). However, if an user hides the menu later and closes the app, the menu will be hidden again with a next start. Just because the app restores the last app state.
