complete doctest stub (#1315)

* complete doctest stub

And merge it into 2and3 (the old stubs were virtually empty).

* note things changed in 3.4

2.7 also had an undocumented and deprecated doctest.Tester class. I'm going to leave it out until somebody asks for it to be added.

stdlib/2/doctest.pyi

@@ -1,9 +0,0 @@
-# Stubs for doctest
-
-# NOTE: These are incomplete!
-
-from typing import Any, Tuple
-
-# TODO arguments missing
-def testmod(m: Any = ..., name: str = ..., globs: Any = ...,
-            verbose: bool = ...) -> Tuple[int, int]: ...