Document the return type when translating Doxygen @return to Python.

In addition to translating the comment itself, also document the type of the
object returned. This is consistent with generating not only :param: but also
:type: for the parameters documented using @param.

Examples/test-suite/python/doxygen_translate_runme.py

@@ -99,10 +99,13 @@ r"""
 
     Another remarks section
 
+    :rtype: int
     :return: Whatever
 
+    :rtype: int
     :return: it
 
+    :rtype: int
     :return: may return
 
     See also: someOtherMethod