Workalendar

- Hotfix: Taiwan exceptional working day on February, 20th 2021 (628).
- Hotfix: September 11th is a working day in Taiwan (628).

Major changes

- API: New method available in `core` module: `Calendar.get_iso_week_date()` to find the weekday X of the week number Y (619).
- Requirements: Replace pytz with `(backports.)zoneinfo`, thx to eumiro (614)
- Doc: Documented the different (in)compatibilities due to the use of `zoneinfo` (614).

Minor changes

Bugfixes

- Small fixes in Netherlands School calendars (619).
- Temporary downgrade of `pyupgrade` to fix the `pyup_dirs`.

Improving test coverage

- Improve Netherlands coverage (546, 619).
- Improve Russia coverage (546).
- Improve USA calendar coverage by removing a method that wasn't used anyways (`get_washington_birthday_december()`). The method is implemented in both Indiana and Georgia State calendars, and is specific for each state, even if they look very similar (546).
- Improve the `astronomy.py` module coverage (546).
- Improve coverage for the `tests/__init__.py` module (546). *Note:* system-dependant test branch (if Windows) won't be counted for coverage.

Calendar change

- Update Malaysia 2022-2024 (Deepavali + Thaipusam) by jack-pace

Calendar changes

- Update Singapore for range from 2022 to 2030 (Deepavali), by hprobotic

Internal changes

- Replace `os.path.*` calls with `pathlib.Path`, thx to eumiro (603)
- Use f-string for string formatting, thx to eumiro (605)
- Simplify collections handling, thx to eumiro (606)
- Use integers for time units divisions, thx to eumiro
- Adding Mac OS & Windows tests to the test matrix (related to 607).
- Fix tests when running them on Windows (607).

- Fix Russia 2021 holidays, thx MichalChromcak for the bug report (578).

Fixes

- Fix Russia calendar: non-working days are shifted to the next MON when they happen on the week-end (589).
- Fix Russia New year holidays. It has become a week off since 2005 (related to 578).
- Added Russia COVID-19 non-working days for the year 2020 ; these days are not shifted to next MON (578).
- Fixed Russia Christmas day ; December 25th is not a public holiday. Fixed several other Orthodox calendars (530).
- Update China's public holidays for 2021, thanks iamsk.

Minor changes

- Added a `daterange` function in `workalendar.core` module to iterate between two dates.