Remove custom Path implementation in favor of PEP428

[codingjoe]

Is there any good reason why this library implements it's own path implementation even tho there is a builtin in Python?
https://docs.python.org/3/library/pathlib.html#module-pathlib
https://www.python.org/dev/peps/pep-0428/

My suggestion would be to replace it, to reduce complexity and avoid people confusing them.

[codingjoe]

I would suggest to deprecate the current path implementation with a warning and update the documentation to use the builtin one.

Oh and I am aware the PEP428 is not implemented in Python 2, but hey it's 2018. Even Django dropped Python 2 support. Do you really still want to support it? If you want to use and old Python and Django version, you are probably good using an old version of this package too.