Make codetools.blocks2 work with python3

Hi, I've understood that modules `codetools.blocks2` and `codetools.blocks` are not working for python3 yet, I'm very interested into this kind of static analysis features, especially the use of [`restrict`](https://github.com/enthought/codetools/blob/96f52148adce62d3eb7c86637663ea21c87eb0cd/codetools/blocks2/tests/test_block.py#L40).

Is there any plan to make it work with python3 ? Do you know what's the effort needed for this migration ? We should port `blocks2` only right?

Tell me what you think,

Thanks