Add minimal setup.py file to make chb pip installable

[waskyo]

With this in place, we can do:

pip install -e chb@git+https://github.com/static-analysis-engineering/CodeHawk-Binary.git

instead of having to mess with $PYTHONPATH.

The -e installs it in editable mode so pip will download new versions as they become available (at least in theory!).