[Update] Documentation for sniff WordPress.Files.FilesName

[jasonkenison]

Related to #1722
Continuing updates from #2492

1. Grouped all checks into individual standards.
2. Included additional standards not previously included
3. Added more check valid and invalid examples

Closes #2492

[rodrigoprimo]

Thanks for working on this PR, @jasonkenison! I left some comments with suggestions. Let me know if you have any questions.

[rodrigoprimo]

@jasonkenison, I was just wondering if you'll have a chance to finish this off in the near future. It would be great if this PR could be included in the next WPCS release.

If you haven't got time or lost interest, please let us know and we'll see if we can find someone to take over. Thanks!

[rodrigoprimo]

@jasonkenison, I reacted with 👍 in the last comment of all the conversations where you already addressed my suggestion. When you have a moment, could you please resolve those? I also replied to your question and provided an example.

I believe there is still one comment that was not addressed: #2590 (comment)

Thanks for your contributions!

[rodrigoprimo]

Thanks for addressing the last comment and for all your work, @jasonkenison! This PR looks good to me.