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.

 know more

Describe your change:

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

Checklist:

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new JavaScript files are placed inside an existing directory.
• 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
• 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)

[appgurueu]

Again sorry for the late reply; this got caught in the Hacktoberfest...

Code-wise this looks okay (formatting nitpick: Why no space before ( for flow control statements?). You should document what exactly this returns, though (sorted array of modes). Where does the "average" in the name come from?

The tests should use it.each.

This is relatively simple, but I think we can include it anyways; it implements an established concept from statistics, and is not too trivial.

[appgurueu]

You could write this as max = Math.max(max, count + 1)