Chapter 6: Recursive Functions

@laurocaetano and @carlosgaldino here are my solutions for chapter 6. The nice thing is that it matched the chapter 2 of Introduction to Algorithms that presents merge sort. Seeing the Recursive + Pattern Matching solution is beautiful and easy to understand as quicksort.
:thumbsup: just checked this definition on chapter4/ex01, and I did without this pattern matching.

But, this is an optimization :trollface: