TypeError: exceptions must derive from BaseException

[Morris-Wei]

https://github.com/RobinDavid/pydes/blob/c6a1f909569cd2d19568709ad1da3a62ccb5d2cf/pydes.py#L155

better to be replaced by: raise Exception("Data size should be multiple of 8")

I'm not sure this error only occurs in python3.6(or pycharm), but it seems more sensible to add exception name before detailed description.