Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/xxlimited.pyi

@@ -0,0 +1,13 @@
+from typing import Any
+
+class Null: ...
+class Str: ...
+
+class Xxo:
+    def demo(self) -> None: ...
+
+class error: ...
+
+def foo(__i: int, __j: int) -> Any: ...
+def new() -> Xxo: ...
+def roj(__b: Any) -> None: ...