pathlib support in pytables
 - [ ] closes #14705 
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master | flake8 --diff``
 - [ ] whatsnew entry

As we talked about on gitter, I added the line (https://github.com/pandas-dev/pandas/blob/master/pandas/io/pytables.py#L266) to the HDFStore.open function. Let me know if I misunderstood or should make further edits, thank you!