use versioneer for version management (#88)

- fix #87
- user versioneer for version management
   - use tag "vMAJOR.MINOR.PATCH" to indicate release number
   - exclude generated files from coverage;
      also exclude tests from coverage reporting;
      allow use of "# pragma: no cover" to exclude lines of code
      from coverage
   - configure coverage with entries in setup.cfg (removed
      commandline config from workflows/python-package.yml)
- related doc updates
   - make docs automatically use current version
      (docs use versioneer-based propka.__version__)
   - also added @IAlibay to authors (forgotten in previous
      PRs #84 and #85)
   - generate a sitemap (add sphinx_sitemap to requirements.txt)
- add test_version
   Note: Versioneer-generated version is “0-untagged” on the branch where
   it is tested so need to add it to a valid result.

.github/workflows/python-package.yml

@@ -37,7 +37,8 @@ jobs:
         flake8 . --count --exit-zero --max-complexity=10 --max-line-length=127 --statistics
     - name: Test with pytest and coverage
       run: |
-        coverage run --source=propka -m pytest
+        # configure coverage with entries in setup.cfg
+        coverage run -m pytest
         coverage report -m | tee coverage.txt
         coverage html
     - name: Upload coverage to https://codecov.io/gh/jensengroup/propka