Pythonic implementation of LRU Cache (#4630)

* Added a more pythonic implementation of LRU_Cache.[#4628]

* Added test cases and doctest

* Fixed doc tests

* Added more tests in doctests and fixed return types fixes [#4628]

* better doctests

* added doctests to main()

* Added dutch_national_flag.py in sorts. fixing [#4636]

* Delete dutch_national_flag.py

incorrect commit

* Update lru_cache_pythonic.py

* Remove pontification

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Co-authored-by: Christian Clauss <cclauss@me.com>