Support pathlib into path.versions functions

[aecorn]

The functions that accept str-paths in, should also allow for pathlib.Path s.

On another note
The function "split_path" was removed, this was in use in at least on case Ive met until now, and removing it was probably a non-intentional breaking change? Removing non-private functions that have been published on Pypi, is usually something you want to avoid unless you are versioning up a whole version.

Reported by @SteffNate