• 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)