Mergesort

[Blackwidow2981]

Implemented Merge Sort algorithm in python

Fixes #344

Checklist:

• [X] I have read the contribution guidelines before making this PR.
• [X] My code follows the style guidelines of this project
• [X] I have performed a self-review of my own code
• [X] I have commented in my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation (Language folder or any other readme instructed to)
• [X] My changes generates no new warnings
• [X] I have added tests that prove my fix is effective or that my feature works

[kaustubhgupta]

Hi @Blackwidow2981, good to see you back. Actually, your PR is conflicting with another readme file. Also, there are a lot of commits that are nowhere related to the issue assigned. I would suggest forking the repo again and then create the PR.