Add stubs for pkgutils (#431)

* py3 done (py2 pass empty)

* remove dangling importlib

* importlib.abc only exists in py3

stdlib/2and3/pkgutil.pyi

@@ -0,0 +1,31 @@
+# Stubs for pkgutil
+
+from typing import Any, Callable, Generator, IO, Iterable, Optional, Tuple
+import sys
+
+if sys.version_info >= (3,):
+    from importlib.abc import Loader
+else:
+    Loader = Any
+
+_YMFNI = Generator[Tuple[Any, str, bool], None, None]
+
+
+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) -> Loader: ...
+def get_importer(path_item: str) -> Any: ...  # TODO precise type
+def get_loader(module_or_name: str) -> Loader: ...
+def iter_importers(fullname: str = ...) -> Generator[Any, None, None]: ...  # TODO precise type
+def iter_modules(path: Optional[str] = ...,
+                 prefix: str = ...) -> _YMFNI: ...  # TODO precise type
+def walk_packages(path: Optional[str] = ..., prefix: str = ...,
+                  onerror: Optional[Callable[[str], None]] = ...) -> _YMFNI: ...
+def get_data(package: str, resource: str) -> bytes: ...