add (overwrite with) mypy stubs, if available

stdlib/2.7/struct.pyi

@@ -0,0 +1,28 @@
+# Stubs for struct for Python 2.7
+# Based on https://docs.python.org/2/library/struct.html
+
+from typing import Any, Tuple
+
+class error(Exception): ...
+
+def pack(fmt: str, *v: Any) -> str: ...
+# TODO buffer type
+def pack_into(fmt: str, buffer: Any, offset: int, *v: Any) -> None: ...
+
+# TODO buffer type
+def unpack(fmt: str, buffer: Any) -> Tuple[Any, ...]: ...
+def unpack_from(fmt: str, buffer: Any, offset: int = ...) -> Tuple[Any, ...]: ...
+
+def calcsize(fmt: str) -> int: ...
+
+class Struct:
+    format = ... # type: str
+    size = ... # type: int
+
+    def __init__(self, format: str) -> None: ...
+
+    def pack(self, *v: Any) -> str: ...
+    # TODO buffer type
+    def pack_into(self, buffer: Any, offset: int, *v: Any) -> None: ...
+    def unpack(self, buffer: Any) -> Tuple[Any, ...]: ...
+    def unpack_from(self, buffer: Any, offset: int = ...) -> Tuple[Any, ...]: ...