Added quicksort C++ - Issue #250

[makjn10]

For short term contributors: we understand that getting your commits well
defined like we require is a hard task and takes some learning. If you
look to help without wanting to contribute long term there's no need
for you to learn this. Just drop us a message and we'll take care of brushing
up your stuff for merge!

Fixes #250

By submitting this pull request I confirm I've read and complied with the
below declarations.

• I have read the Contribution guidelines and I am confident that my PR reflects them.
• I have followed the commit guidelines for this project.
• My code follows the standard code structure.
• This pull request has a descriptive title. For example, {Tag}: Add {Algorithm/DS name} [{Language}], not Update README.md or Added new code.
• This pull request will be closed if I fail to update it even once in a continuous time span of 7 days.
• This pull request shall only be reviewed and merged once all the checks passes. No maintainer or supporter shall be obliged to review it before this condition is met.
• I have mentioned the issue number correctly (with hyperlink) in this pull request description.

After you submit your pull request, DO NOT click the 'Update Branch' button.