Add mailcap module (#3482)

Author: CraftSpider

stdlib/2and3/mailcap.pyi

@@ -0,0 +1,7 @@
+
+from typing import Sequence, Dict, List, Union, Tuple, Optional, Mapping
+
+_Cap = Dict[str, Union[str, int]]
+
+def findmatch(caps: Mapping[str, List[_Cap]], MIMEtype: str, key: str = ..., filename: str = ..., plist: Sequence[str] = ...) -> Tuple[Optional[str], Optional[_Cap]]: ...
+def getcaps() -> Dict[str, List[_Cap]]: ...