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.

tests/test_version.py

@@ -0,0 +1,10 @@
+import propka
+import re
+
+def test_version_exists():
+    assert hasattr(propka, '__version__')
+
+def test_version():
+    assert (re.match(r'[0-9]+\.[0-9]+', propka.__version__) or
+            propka.__version__.startswith('0+untagged'))
+