Pystatis

- support new Zensus 2022 web interface / API by changing base_url in default config to new value <https://ergebnisse.zensus2022.de/api/rest/2020/>
- users have to either update or delete their old config, detailed instructions are added to the README
- for some tables, the regional code can change, all rows except one might be KREISE but one is DG for Germany, fixed this so we still output AGS column
- added missing regional codes that were introduced by Zensus 2022

- support a wide range of parameters for `get_data()`, see API documentation for details -> [PR 64](https://github.com/CorrelAid/pystatis/pull/64)
- support quality symbols with `quality` parameter and improve handling of missing values -> [PR 117](https://github.com/CorrelAid/pystatis/pull/117)
- for all tables with regional codes always include an AGS column with official municipality codes (AGS) -> [PR 123](https://github.com/CorrelAid/pystatis/pull/123)
- improve test suite quality and introduce proper end-to-end tests -> [PR 99](https://github.com/CorrelAid/pystatis/pull/99)
- handle support for languages "en" and "de" -> [PR 58](https://github.com/CorrelAid/pystatis/pull/58)

- remove support for Cube until requested
- add multi database support: Table class accepts any EVAS as `name` parameter without the need to specify the database
- `setup_credentials` can be used to set up credentials for all three supported databases
- Improve Table data format: prettify the raw table format and improve readability
- support new zip format returned by Zensus
- add proper documentation (using Sphinx)