Greetings.

I think it'd be nice to have the ability to subscript/slice instances of pathlib.PurePath and its subclasses e.g.

    path = Path()
    assert path[n:m:k] == type(path)(*path.parts[n:m:k])

Maybe it's worth adding some check with custom exception thrown in case of invalid index/slice. What do you think? I'll open new issue and submit a patch if you approve of this...