Add stubs for importlib.__init__

Part of python#189

stdlib/3/importlib/__init__.pyi

@@ -0,0 +1,23 @@
+import sys
+import types
+from typing import Any, Mapping, Optional, Sequence
+
+
+def __import__(name: str, globals: Mapping[str, Any] = None,
+               locals: Mapping[str, Any] = None, fromlist: Sequence[str] = (),
+               level: int = 0) -> types.ModuleType: ...
+
+
+def import_module(name: str, package: str = None) -> types.ModuleType: ...
+
+
+if sys.version_info >= (3, 3):
+    # Optionally returns a loader, but importlib.abc doesn't have a stub file.
+    def find_loader(name: str, path: str = None): ...
+
+
+    def invalidate_caches() -> None: ...
+
+
+if sys.version_info >= (3, 4):
+    def reload(module: types.ModuleType) -> types.ModuleType: ...