Add support for Path objects for filenames

[ziima]

It would be nice to have support of Path objects for filenames.

[wbond]

I'm open to someone implementing this if it is done in a way that doesn't cause issues with Python 2, which this still supports.

[deathaxe]

It would be straight forward with python 3.8, but as none of the default APIs of python 3.3 supports pathlib, it would add more hazzle, than it would ease things - especially as py33 and py38 would need to be treated differently here and there.