Unit tests comments compliance

[vkresch]

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This PR is a refactoring of test_cases.py and test_cases_doc.py and uses the builtin python unit testing framework to test the compliance of OSI comments. The test cases are implemented in a modular way which is easy maintainable and extensible with more test cases based on categories such as tabs, comments, messages, etc.. Using the unit testing framework will improve the code quality output of the OSI project.

The .travis.yml contains now the command python -m unittest discover tests which runs the unit tests.

This PR also corrects a small typo of the enum Fog from FOG_UNKOWN --> FOG_UNKNOWN.

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@jdsika pls review and let me know your thoughts.

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• My code and comments follow the style guidelines and contributors guidelines of this project.
• I have performed a self-review of my own code.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests / travis ci pass locally with my changes.

[jdsika]

Jesus, well spotted!

[jdsika]

LGTM