Move contents of builtins/* to stdlib/*. This simplifies finding stubs.

stdlib/2.7/cPickle.pyi

@@ -0,0 +1,19 @@
+from typing import Any, IO, List
+
+HIGHEST_PROTOCOL = ...  # type: int
+compatible_formats = ...  # type: List[str]
+format_version = ...  # type: str
+
+class Pickler: ...
+class Unpickler: ...
+
+def dump(obj: Any, file: IO[str], protocol: int = ...) -> None: ...
+def dumps(obj: Any, protocol: int = ...) -> str: ...
+def load(file: IO[str]) -> Any: ...
+def loads(str: str) -> Any: ...
+
+class PickleError(Exception): ...
+class UnpicklingError(PickleError): ...
+class BadPickleGet(UnpicklingError): ...
+class PicklingError(PickleError): ...
+class UnpickleableError(PicklingError): ...