Reconsider use of `__all__` in `__init__`

[MatthewHambley]

This just seems to be a mechanism to cause problems. The saving in typing doesn't seem worth the effort.

[hiker]

While I like the fact that it saves typing a bit (and makes other applications a tiny bit less dependent on implementation details like file location), it is not that much. But out of interest: what are the problems caused by all?

[hiker]

I think this is now a duplicate of #492 , so I am closing this as duplicate, since #492 has already a PR to improve this. We are actually now having similar issues in PSyclone since we started to add typing (before I think all was good).