Nlp-api

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* Replaced unittest with pytest.
* Put the /help endpoint in its own method.
* Added the original text to the returned json.
* Implemented constants in nlp_api and abstract_action.
* Added docstrings where needed, updated documentation examples.

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* Bugfix re: ImportError.

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* Bugfix re: argparse.
* Added help/descriptions, available via -h option.

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* Removing some testing code which accidentally made it into 0.4.0.

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* Added verbose (-v, --verbose) command line option for logging.
* Output of Consolidation and Content Reversal actions is now sorted by how long the value lists are.
* Altered test_nlp_api so it determines when the endpoints are ready for testing rather than sleeping.
* Now accepts multiple texts.

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* Added history to returned content.