Merge "Enable some off-by-default checks"

tox.ini

@@ -43,6 +43,9 @@ commands =
     python setup.py build_sphinx
 
 [flake8]
+# H106: Don’t put vim configuration in source files
+# H203: Use assertIs(Not)None to check for None
+enable-extensions=H106,H203
 show-source = true
 builtins = _
 exclude=.venv,.git,.tox,dist,doc,*lib/python*,*egg,tools