Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/gc.pyi

@@ -0,0 +1,25 @@
+from typing import Any, List, Tuple
+
+def enable() -> None: ...
+def disable() -> None: ...
+def isenabled() -> bool: ...
+def collect(generation: int = ...) -> int: ...
+def set_debug(flags: int) -> None: ...
+def get_debug() -> int: ...
+def get_objects() -> List[Any]: ...
+def set_threshold(threshold0: int, threshold1: int = ..., threshold2: int = ...) -> None: ...
+def get_count() -> Tuple[int, int, int]: ...
+def get_threshold() -> Tuple[int, int, int]: ...
+def get_referrers(*objs: Any) -> List[Any]: ...
+def get_referents(*objs: Any) -> List[Any]: ...
+def is_tracked(obj: Any) -> bool: ...
+
+garbage: List[Any]
+
+DEBUG_STATS: int
+DEBUG_COLLECTABLE: int
+DEBUG_UNCOLLECTABLE: int
+DEBUG_INSTANCES: int
+DEBUG_OBJECTS: int
+DEBUG_SAVEALL: int
+DEBUG_LEAK: int