Re-organize directory structure (#4971)

See discussion in #2491

Co-authored-by: Ivan Levkivskyi <ilevkivskyi@dropbox.com>

stdlib/@python2/dircache.pyi

@@ -0,0 +1,8 @@
+from typing import List, MutableSequence, Text, Union
+
+def reset() -> None: ...
+def listdir(path: Text) -> List[str]: ...
+
+opendir = listdir
+
+def annotate(head: Text, list: Union[MutableSequence[str], MutableSequence[Text], MutableSequence[Union[str, Text]]]) -> None: ...