Tidied up invocations, making InvokeFunction, InvokeRef and Subprogram have
explicit initialisation parameters which help to document the range of
attributes available on those nodes.
1l=[(0,10),(10,20)] 2y=23 3fora,binl: 4foriina,b: 5x=i 6else:# NOTE: Need to support StopIteration! 7x=y 8else: 9a=b