py-cf-units: new package (#11891)

* py-cf-units: new package

* py-cf-units: download from pypi.io

* py-cf-units: include py-pytest-runner as build dep

* py-cf-units: remove empty build_args function

* py-cf-units: fix for flake8

* py-cf-units: indent docstring

* py-cf-units: remove excess spaces

* py-cf-units: list master branch ahead of numeric versions

* py-cf-units: remove extension keyword from version