0.6.2

• Add --python option for nbstripout --install to allow overriding the Python interpreter specified in .git/config (@nobodyinperson, #181, #182)
• Add option --keep-metadata-keys to keep specific metadata keys that are stripped by default (@davidxia, #177, #78)
• Replace Cram as test runner for integration tests with a custom framework which also supports testing on Windows (@arobrien, #176, #178)
• Use SystemExit instead of sys.exit and do not exit from functions (@janosh, #173)