Travis CI: Run black, doctest, flake8, mypy, and pytest (#964)

* Travis CI: Add type checking with mypy

* Create requirements.txt

* script: mypy --ignore-missing-stubs=cv2,numpy .

* Delete requirements.txt

* script: mypy --ignore-missing-imports .

* Run doctests

* Disable doctest -v other/detecting_english_programmatically.py

* Pytest

* No |

* pytest || true

* Run black doctest flake8 mypy pytest

* after_success: Build Directory.md

* Typo in filename: Dictionary.txt --> dictionary.txt'

Discovered via doctest run in #964

* python -m doctest -v

* pip install black flake8 mypy pytest

* pytest --doctest-glob='*.py'

* pytest --doctest-modules

* pytest --doctest-modules ./sorts

* pytest --doctest-modules ./ciphers ./other ./searches ./sorts ./strings || true

* if __name__ == "__main__":

* if __name__ == "__main__":

* if __name__ == '__main__':

* if __name__ == '__main__':

* if __name__ == '__main__':

* Create requirements.txt

* Update requirements.txt

* if __name__ == "__main__":

* Lose the doctests

* if __name__ == '__main__':

* Remove print-a-tuple

* doctest: Added missing spaces

* Update tabu_search.py

* The >>> are not doctests so change to >>)

* Travis CI: Run black, doctest, flake8, mypy, and pytest

* Link to the separate DIRECTORY.md file

* Update README.md