Implement Merge Sort in C++

[VamsiSangam]

Issue Description

• Need the C++ implementation of Merge sort algorithm.
• Corresponding post on website
• Permitted languages - C++

Guidelines

• Your code will be live on a tutorial website, so code readability and understandability will be given paramount importance.
• Please follow coding conventions listed in CONVENTIONS.md
• The directory structure of the project is pretty obvious, but take a moment to go through STRUCTURE.md if you are confused where to place your code.
• Please add a few sample input output test case files too. Minimum 1. The more the merrier!

[sbshah97]

Can I work on this Issue?

[VamsiSangam]

Your enthusiasm for contributing is very welcomed, but you have pending issues. Please complete all pending issues before claiming another. Lets follow this rule so that others can have a chance to issues as well :sweat_smile: . I hope you understand.