docs: adjust sphinx to flask 2

* Add werkzeug to intersphinx for additional type hints
* Describe type hints in bullet points rather than function signatures
* Remove 'warnings as errors' flag from documentation building, as some type hints aren't resolved properly and result in a warning

docs/conf.py

@@ -332,6 +332,8 @@ texinfo_documents = [
 # Example configuration for intersphinx: refer to the Python standard library.
 intersphinx_mapping = {
     "python": ("https://docs.python.org/", None),
+    'flask': ('https://flask.palletsprojects.com/', None),
+    'werkzeug': ('https://werkzeug.palletsprojects.com/', None),
     # TODO: Configure external documentation references, eg:
     # 'Flask-Admin': ('https://flask-admin.readthedocs.io/en/latest/', None),
 }