add rlcompleter (#455)

stdlib/2and3/rlcompleter.pyi

@@ -0,0 +1,13 @@
+# Stubs for rlcompleter
+
+from typing import Optional, Union
+import sys
+
+if sys.version_info >= (3,):
+    _Text = str
+else:
+    _Text = Union[str, unicode]
+
+
+class Completer:
+    def complete(self, text: _Text, state: int) -> Optional[str]: ...