Path objects not supported in low-level I/O packages #4412

In at least io.ascii and io.fits (and perhaps io.votable) one gets unexpected exceptions if a Python 3 Path object is passed as the file name. This was first noted in #4405, where a partial fix was put in place in the I/O registry layer to translate a Path object to a string.

In general a Path object should be accepted anywhere a file object is accepted. At least that would be the theory, with no idea of the difficulty and implications.