Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/@python2/StringIO.pyi

@@ -0,0 +1,28 @@
+from typing import IO, Any, AnyStr, Generic, Iterable, Iterator, List, Optional
+
+class StringIO(IO[AnyStr], Generic[AnyStr]):
+    closed: bool
+    softspace: int
+    len: int
+    name: str
+    def __init__(self, buf: AnyStr = ...) -> None: ...
+    def __iter__(self) -> Iterator[AnyStr]: ...
+    def next(self) -> AnyStr: ...
+    def close(self) -> None: ...
+    def isatty(self) -> bool: ...
+    def seek(self, pos: int, mode: int = ...) -> int: ...
+    def tell(self) -> int: ...
+    def read(self, n: int = ...) -> AnyStr: ...
+    def readline(self, length: int = ...) -> AnyStr: ...
+    def readlines(self, sizehint: int = ...) -> List[AnyStr]: ...
+    def truncate(self, size: Optional[int] = ...) -> int: ...
+    def write(self, s: AnyStr) -> int: ...
+    def writelines(self, iterable: Iterable[AnyStr]) -> None: ...
+    def flush(self) -> None: ...
+    def getvalue(self) -> AnyStr: ...
+    def __enter__(self) -> Any: ...
+    def __exit__(self, type: Any, value: Any, traceback: Any) -> Any: ...
+    def fileno(self) -> int: ...
+    def readable(self) -> bool: ...
+    def seekable(self) -> bool: ...
+    def writable(self) -> bool: ...