reworked Documentation

The documenation now has a new theme and updated apidocs.
Also the main index is built from the README.md contents.

docs/clean_docs.py

@@ -6,17 +6,17 @@ This is needed if the Python source being documented changes significantly. Old
 RST files can be left behind.
 """
 
-from pathlib import Path
 import shutil
+from pathlib import Path
 
 
 def main() -> None:
     docs_dir = Path(__file__).resolve().parent
-    for folder in ("_build", "apidoc"):
+    for folder in ('build', 'source/apidoc'):
         delete_dir = docs_dir / folder
         if delete_dir.exists():
             shutil.rmtree(delete_dir)
 
 
-if __name__ == "__main__":
+if __name__ == '__main__':
     main()