Nebuchadnezzar

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- Add Basic Auth authentication to publish

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- Update cnxml for >=2.2.0 (74)

- allow non-descendent path to xml in error output

- update expected test output for new jing

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- Update tests to match new error messages from cnxml v2.2.0

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- Add content*.cnx.org environments to the default configuration file.

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- Fix ``FileNotFoundError`` raised on on user's first run of Nebuchadnezzar.
This was caused by the parent directory not existing, so the default
behavior of writing the default config failed with this error.
See https://github.com/Connexions/nebuchadnezzar/issues/66

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- Split the cli module into submodules, one for each subcommmand.

- Add a skip-validation option flag to the publish command.

- Suggest a newer version of Neb to install on ``--version`` when
it is determined that the user's version is older than the last
release.
See https://github.com/Connexions/nebuchadnezzar/issues/16

- Resource/image files will no longer be copied into the working
directory when using ``neb get``.
See https://github.com/Connexions/nebuchadnezzar/issues/61