Fix long line, tests (#2123)

* Fix long line

* updating DIRECTORY.md

* Add doctest

* ...

* ...

* Update tabu_search.py

* space

* Fix doctest

    >>> find_neighborhood(['a','c','b','d','e','a'])  # doctest: +NORMALIZE_WHITESPACE
    [['a','e','b','d','c','a',90], [['a','c','d','b','e','a',90],
     ['a','d','b','c','e','a',93], ['a','c','b','e','d','a',102],
     ['a','c','e','d','b','a',113], ['a','b','c','d','e','a',93]]

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>
Co-authored-by: John Law <johnlaw.po@gmail.com>