add Python 2 stubs for ast, tokenize

stdlib/2.7/ast.pyi

@@ -0,0 +1,28 @@
+# Automatically generated by pytype. May contain errors.
+
+from typing import Any, Tuple, Generator
+
+from _ast import *
+
+__version__ = ...  # type: int
+PyCF_ONLY_AST = ...  # type: int
+
+def copy_location(new_node, old_node) -> Any: ...
+def dump(node, *args, **kwargs) -> str: ...
+def fix_missing_locations(node) -> Any: ...
+def get_docstring(node, *args, **kwargs) -> Any: ...
+def increment_lineno(node, *args, **kwargs) -> Any: ...
+def iter_child_nodes(node) -> Generator[Any, Any, Any]: ...
+def iter_fields(node) -> Any: ...  # TODO: Generator[Tuple[Any, ...]]: ...
+def literal_eval(node_or_string) -> Any: ...
+def parse(source, filename, mode, *args, **kwargs) -> Any: ...
+def walk(node) -> Any: ...  # TODO: Generator[Any]: ...
+
+class NodeVisitor(object):
+    __doc__ = ...  # type: str
+    def generic_visit(self, node) -> None: ...
+    def visit(self, node) -> Any: ...
+
+class NodeTransformer(NodeVisitor):
+    __doc__ = ...  # type: str
+    def generic_visit(self, node) -> Any: ...