Added Burkes dithering algorithm. (#1916)

* Added Burkes dithering algorithm

* Added unit tests for burkes algorithm

* Fix burkes algorithm

* Added some additional information

* Fixed CI tests

* Update digital_image_processing/dithering/burkes.py

Co-Authored-By: Christian Clauss <cclauss@me.com>

* Update digital_image_processing/dithering/burkes.py

Co-Authored-By: Christian Clauss <cclauss@me.com>

* Update digital_image_processing/dithering/burkes.py

Co-Authored-By: Christian Clauss <cclauss@me.com>

* Propogate the += and add a doctest

* Fix doctest

* @staticmethod --> @ classmethod to ease testing

* def test_burkes(file_path):

* Fix for mypy checks

* Fix variable order in get_greyscale

* Fix get_greyscale method

* Fix get_greyscale method

* 3.753

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