* Remove redundant wheel dep from pyproject.toml

   Remove the redundant `wheel` dependency, as it is added by the backend
automatically.  Listing it explicitly in the documentation was
a historical mistake and has been fixed since, see:
pypa/setuptools@f7d30a9

* Add build into deps (prepare-dist)

Co-authored-by: Tom Schraitle <[email protected]>

correct typo in function description of `next_version`

* Set timeout-minutes ti 15min
* Add on.push.path on.pull_request.path
* Raise Python 3.7 -> 3.8
* Use cache for actions/setup-python@v3

Improve GitHub Action

Benefits:
* Users of our software can easily cite it using the metadata from
  CITATION.cff
* GitHub shows the citation information in the sidebar
* Browser plugins can import the correct reference

Sources:
* https://citation-file-format.github.io/
* https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-citation-files

Add CITATION.cff for citation

* Export all semver names in `__all__` variable.
* Fix linting issues

* Add config options to pyproject.toml
* Call docformatter without any options in tox.ini
  as they are set in pyproject.toml now

* Raise version
* Ignore exit code from docformatter in checks `tox.ini`
* Correct typo in release-procedure.md
* Update CHANGELOG.rst