Vito

* Deprecated functionality is removed (workarounds for Python versions older than 3.6).
* Most frequently used methods now have type hints.
* Parameter order check to imsave (that's the one thing I alwys mess up when coding without IDE).
* `imsave` now creates the output directory structure if it did not exist.

* Silences the log messages upon import
* `imshow` falls back to PIL if opencv is compiled without GUI dependencies
* Include recent python version in python packaging tests

f-strings require at least Python 3.6, needed to revert the string formatting