Drop Python2 support (and python code style testing)
Hello @isolov, @avolio and @akazarov,
please accept this merge request.
It implements two main changes:
- it drops the support for Python2 and in particular it gets rid of a hack which was needed to concurrently support statements with incompatible syntax in Python2 and Python3
- it includes a new test validating the python codes style
Thanks. Cheers Wainer