Re-organize directory structure (#4971)

See discussion in #2491

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

stdlib/struct.pyi

@@ -0,0 +1,38 @@
+import sys
+from array import array
+from mmap import mmap
+from typing import Any, Iterator, Text, Tuple, Union
+
+class error(Exception): ...
+
+_FmtType = Union[bytes, Text]
+if sys.version_info >= (3,):
+    _BufferType = Union[array[int], bytes, bytearray, memoryview, mmap]
+    _WriteBufferType = Union[array, bytearray, memoryview, mmap]
+else:
+    _BufferType = Union[array[int], bytes, bytearray, buffer, memoryview, mmap]
+    _WriteBufferType = Union[array[Any], bytearray, buffer, memoryview, mmap]
+
+def pack(fmt: _FmtType, *v: Any) -> bytes: ...
+def pack_into(fmt: _FmtType, buffer: _WriteBufferType, offset: int, *v: Any) -> None: ...
+def unpack(__format: _FmtType, __buffer: _BufferType) -> Tuple[Any, ...]: ...
+def unpack_from(__format: _FmtType, buffer: _BufferType, offset: int = ...) -> Tuple[Any, ...]: ...
+
+if sys.version_info >= (3, 4):
+    def iter_unpack(__format: _FmtType, __buffer: _BufferType) -> Iterator[Tuple[Any, ...]]: ...
+
+def calcsize(__format: _FmtType) -> int: ...
+
+class Struct:
+    if sys.version_info >= (3, 7):
+        format: str
+    else:
+        format: bytes
+    size: int
+    def __init__(self, format: _FmtType) -> None: ...
+    def pack(self, *v: Any) -> bytes: ...
+    def pack_into(self, buffer: _WriteBufferType, offset: int, *v: Any) -> None: ...
+    def unpack(self, __buffer: _BufferType) -> Tuple[Any, ...]: ...
+    def unpack_from(self, buffer: _BufferType, offset: int = ...) -> Tuple[Any, ...]: ...
+    if sys.version_info >= (3, 4):
+        def iter_unpack(self, __buffer: _BufferType) -> Iterator[Tuple[Any, ...]]: ...