feat: added implementation for average mode

[SpiderMath]

This pull request aims to add the implementation for Average Mode I did not however run npm run test, for it seems it modified over 700 files, many of which I didn't understand the reason for. Hence I just tried to stick to the standards by myself as much as I could.

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Describe your change:

• [x] Add an algorithm?
• [ ] Fix a bug or typo in an existing algorithm?
• [ ] Documentation change?

Checklist:

• [x] I have read CONTRIBUTING.md.
• [x] This pull request is all my own work -- I have not plagiarized.
• [x] I know that pull requests will not be merged if they fail the automated tests.
• [x] This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• [x] All new JavaScript files are placed inside an existing directory.
• [x] All filenames should use the UpperCamelCase (PascalCase) style. There should be no spaces in filenames. Example:UserProfile.js is allowed but userprofile.js,Userprofile.js,user-Profile.js,userProfile.js are not
• [x] All new algorithms have a URL in their comments that points to Wikipedia or another similar explanation.
• [ ] If this pull request resolves one or more open issues then the commit message contains Fixes: #{$ISSUE_NO}.

[SpiderMath]

@appgurueu and @raklaptudirm, sorry to ping, but could you please check this PR maybe? 😅

[SpiderMath]

Hello? Anyone here? @appgurueu & @raklaptudirm?

[raklaptudirm]

Hmm I think this algorithm may be too trivial to warrant inclusion in the repo. @appgurueu what do you think?

[SpiderMath]

Any updates? (I was away for a while)