Fix positioning of <a> tags relative to headers

[lachlancollins]

No new line above Markdown headings is considered invalid in some compilers, including Docusaurus. This PR simply moves the <a> tags below the headers, which was already the format used in some files (such as Decorators.md).

EDIT: I also fixed an <a> link which could have been written as a Markdown ([text](url)) link in Server.md.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[Eomm]

What about older documentation in v1 and v2 branches?
We need to update those links as well or there is a way to bypass this issue on docusaurus side?

[lachlancollins]

@Eomm yep we have a solution to this - @climba03003 proposed pushing the changes to the 1.x and 2.x branches in this repo. I've already done the necessary changes here, but I just haven't created the PRs because I didn't want to submit multiple at once! Would you like me to submit those now?

[Eomm]

Oh, just asking, no pressure at all!

[lachlancollins]

@Eomm I've made the PRs now if you want to have a look :) #3494 and #3495

[mcollina]

lgtm

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