* Python 2.7 only release, to make `pip install nbstripout` work in Python 2.7
(previously, this was picking up 0.3.8 which is *not* Python 2.7 compatible)
* Drop Python 3.4 support, add support for Python 3.7, 3.8
* Windows compatibility: "" quote Python interpreter path (115, fcollonval)
* Add `--dry-run` flag (122)
* Support specifying `keep_output` as a cell tag (117, scottcode)