Merge Sort[cpp]

[Acepatil]

This issue is about [Merge Sort](link to resource for the Algo/DS).

• [x] Issue Title is in form Algo/DS Name [Language].
• [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
• [x] This Algo/DS is worth adding to this repository.
• [x] Assign this issue to me (I want to work on this).
  • [x] I ensure that I am not already assigned to 2 or more issues.
• [x] I will send my PR only after I'm assigned to this issue by any maintainer.
• [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

I wish to add merge sort in cpp @iiitv/algo-maintainers

[aspiringgarv]

Hey could you assign this to me

[raj-j-shah]

@Acepatil do not create duplicate issues.This issue already exists (#850) .