Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/pkgutil.pyi

@@ -0,0 +1,38 @@
+import sys
+from _typeshed import SupportsRead
+from typing import IO, Any, Callable, Iterable, Iterator, NamedTuple, Optional, Tuple, Union
+
+if sys.version_info >= (3,):
+    from importlib.abc import Loader, MetaPathFinder, PathEntryFinder
+else:
+    Loader = Any
+    MetaPathFinder = Any
+    PathEntryFinder = Any
+
+if sys.version_info >= (3, 6):
+    class ModuleInfo(NamedTuple):
+        module_finder: Union[MetaPathFinder, PathEntryFinder]
+        name: str
+        ispkg: bool
+    _ModuleInfoLike = ModuleInfo
+else:
+    _ModuleInfoLike = Tuple[Union[MetaPathFinder, PathEntryFinder], str, bool]
+
+def extend_path(path: Iterable[str], name: str) -> Iterable[str]: ...
+
+class ImpImporter:
+    def __init__(self, dirname: Optional[str] = ...) -> None: ...
+
+class ImpLoader:
+    def __init__(self, fullname: str, file: IO[str], filename: str, etc: Tuple[str, str, int]) -> None: ...
+
+def find_loader(fullname: str) -> Optional[Loader]: ...
+def get_importer(path_item: str) -> Optional[PathEntryFinder]: ...
+def get_loader(module_or_name: str) -> Loader: ...
+def iter_importers(fullname: str = ...) -> Iterator[Union[MetaPathFinder, PathEntryFinder]]: ...
+def iter_modules(path: Optional[Iterable[str]] = ..., prefix: str = ...) -> Iterator[_ModuleInfoLike]: ...
+def read_code(stream: SupportsRead[bytes]) -> Any: ...  # undocumented
+def walk_packages(
+    path: Optional[Iterable[str]] = ..., prefix: str = ..., onerror: Optional[Callable[[str], None]] = ...
+) -> Iterator[_ModuleInfoLike]: ...
+def get_data(package: str, resource: str) -> Optional[bytes]: ...