Create quicksort.cpp

[neelabhtiwari]

quicksort.cpp Add QuickSort Algorithm

This adds QuickSort Algorithm which return the concatenation of the
quicksorted list of elements that are less than or equal to the pivot, the
pivot, and the quicksorted list of elements that are greater than the pivot.

Closes #250

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Fixes #{ISSUE_NUMBER}

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[sangamcse]

Duplicate of #255