Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/cStringIO.pyi

@@ -0,0 +1,48 @@
+from abc import ABCMeta
+from types import TracebackType
+from typing import IO, Iterable, Iterator, List, Optional, Union, overload
+
+# This class isn't actually abstract, but you can't instantiate it
+# directly, so we might as well treat it as abstract in the stub.
+class InputType(IO[str], Iterator[str], metaclass=ABCMeta):
+    def getvalue(self) -> str: ...
+    def close(self) -> None: ...
+    @property
+    def closed(self) -> bool: ...
+    def flush(self) -> None: ...
+    def isatty(self) -> bool: ...
+    def read(self, size: int = ...) -> str: ...
+    def readline(self, size: int = ...) -> str: ...
+    def readlines(self, hint: int = ...) -> List[str]: ...
+    def seek(self, offset: int, whence: int = ...) -> int: ...
+    def tell(self) -> int: ...
+    def truncate(self, size: Optional[int] = ...) -> int: ...
+    def __iter__(self) -> InputType: ...
+    def next(self) -> str: ...
+    def reset(self) -> None: ...
+
+class OutputType(IO[str], Iterator[str], metaclass=ABCMeta):
+    @property
+    def softspace(self) -> int: ...
+    def getvalue(self) -> str: ...
+    def close(self) -> None: ...
+    @property
+    def closed(self) -> bool: ...
+    def flush(self) -> None: ...
+    def isatty(self) -> bool: ...
+    def read(self, size: int = ...) -> str: ...
+    def readline(self, size: int = ...) -> str: ...
+    def readlines(self, hint: int = ...) -> List[str]: ...
+    def seek(self, offset: int, whence: int = ...) -> int: ...
+    def tell(self) -> int: ...
+    def truncate(self, size: Optional[int] = ...) -> int: ...
+    def __iter__(self) -> OutputType: ...
+    def next(self) -> str: ...
+    def reset(self) -> None: ...
+    def write(self, b: Union[str, unicode]) -> int: ...
+    def writelines(self, lines: Iterable[Union[str, unicode]]) -> None: ...
+
+@overload
+def StringIO() -> OutputType: ...
+@overload
+def StringIO(s: str) -> InputType: ...