Update mypy to the latest

This includes updating the ignore comments for things which mypy
now knows about or now complains about, as well as pulling in some
typeshed packages for things outside the standard library.

setup.cfg

@@ -28,6 +28,9 @@ max-line-length = 100
 
 
 [mypy]
+# Exclude our copies of external stubs
+exclude = ^jedi/third_party
+
 # Ensure generics are explicit about what they are (e.g: `List[str]` rather than
 # just `List`)
 disallow_any_generics = True