Revert "Clean up sudoku.py."

This reverts commit 795d6b75d782e1b59ba25748b212e7e2aded2480.
Revert 795d6b7..fcb1b54

This rolls back to commit 795d6b75d782e1b59ba25748b212e7e2aded2480.
Optimised QuickSort.

Made it clearer.
Add a simpler MergeSort
Move sudoku under quiz.