Split stdlib into Python 2 and 3 versions (#5442)

All new files in stdlib/@python2 are straight copies of the
corresponding files in stdlib.

stdlib/@python2/netrc.pyi

@@ -0,0 +1,17 @@
+from _typeshed import AnyPath
+from typing import Dict, List, Optional, Tuple
+
+class NetrcParseError(Exception):
+    filename: Optional[str]
+    lineno: Optional[int]
+    msg: str
+    def __init__(self, msg: str, filename: Optional[AnyPath] = ..., lineno: Optional[int] = ...) -> None: ...
+
+# (login, account, password) tuple
+_NetrcTuple = Tuple[str, Optional[str], Optional[str]]
+
+class netrc:
+    hosts: Dict[str, _NetrcTuple]
+    macros: Dict[str, List[str]]
+    def __init__(self, file: Optional[AnyPath] = ...) -> None: ...
+    def authenticators(self, host: str) -> Optional[_NetrcTuple]: ...