add (overwrite with) mypy stubs, if available

stdlib/2.7/base64.pyi

@@ -0,0 +1,25 @@
+# Stubs for base64
+
+# Based on http://docs.python.org/3.2/library/base64.html
+
+from typing import IO
+
+def b64encode(s: str, altchars: str = None) -> str: ...
+def b64decode(s: str, altchars: str = None,
+              validate: bool = False) -> str: ...
+def standard_b64encode(s: str) -> str: ...
+def standard_b64decode(s: str) -> str: ...
+def urlsafe_b64encode(s: str) -> str: ...
+def urlsafe_b64decode(s: str) -> str: ...
+def b32encode(s: str) -> str: ...
+def b32decode(s: str, casefold: bool = False,
+              map01: str = None) -> str: ...
+def b16encode(s: str) -> str: ...
+def b16decode(s: str, casefold: bool = False) -> str: ...
+
+def decode(input: IO[str], output: IO[str]) -> None: ...
+def decodebytes(s: str) -> str: ...
+def decodestring(s: str) -> str: ...
+def encode(input: IO[str], output: IO[str]) -> None: ...
+def encodebytes(s: str) -> str: ...
+def encodestring(s: str) -> str: ...