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.cfg

@@ -1,2 +1,24 @@
 [bdist_wheel]
 universal=1
+
+[versioneer]
+VCS = git
+style = pep440
+versionfile_source = propka/_version.py
+versionfile_build = propka/_version.py
+tag_prefix = v
+parentdir_prefix = propka-
+
+
+[coverage:run]
+source = propka
+omit =
+    # exclude versioneer generated file
+    propka/_version.py
+    # do not cover tests (already covered with source = propka)
+    tests/*
+    
+[coverage:report]
+exclude_lines =
+    pragma: no cover
+