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.

setup.py

@@ -2,12 +2,13 @@
 # PROPKA 3
 
 from setuptools import setup, find_packages
+import versioneer
 
-VERSION = "3.2.0"
 
 setup(
     name="propka",
-    version=VERSION,
+    version=versioneer.get_version(),
+    cmdclass=versioneer.get_cmdclass(),
     description="Heuristic pKa calculations with ligands", long_description="""
 PROPKA predicts the pKa values of ionizable groups in proteins (version 3.0) and
 protein-ligand complexes (version 3.1 and later) based on the 3D structure.