[PyCrust] Significant refactoring

[Chin H. W. <ch...@ix...>]

I just download the PyCrust-0.5.3 and the demos/PyCrustAlaCarte is now
broken due to the non-existence of Editor class and module. My plan is to
subclass Interpreter class. But because the Editor class is gone and with it
the writeOut, writeErr, and readIn has been moved to Shell class. So what is
the RIGHT way of subclassing the Interpreter class?