Update links from "broken" to "not 404, but not very useful either."

[Quuxplusone]

The pointed-to documentation seems to be (A) gone and (B) obsolete. I've fixed the first problem, but the second problem requires someone to write the docs that have been "uncer construction" for a while now.

[dpvc]

Thanks for your interest in helping us maintain the documentation for MathJax. It turns out, however, that the main issue here is that this repository is for MathJax v2, and the current MathJax documentation is for v3, so the link went to the wrong version of the documentation. The correct link would be to en/v2.7-latest rather than en/latest.

Similarly, the page you link to fo extension examples is to the version 3 examples, rather than version 2 ones.

That distinction needs to be made clear, so I will modify the README page to indicate that this is a version 2 repository, and point to the v2 documentation. Since I will be updating the links while I do that, I will close this PR, but with appreciation for your pointing gout the problem.

[Quuxplusone]

Sounds good!

Do you know if there exists a similar repo or documentation for MathJax v3? I'm looking for any foothold re https://stackoverflow.com/questions/63428119/upgrading-from-mathjax-2-7-5-to-3-0-trying-to-preserve-a-custom-tex-environment

[dpvc]

Your question is on my list, but I haven't gotten to it yet. Better support for this does need to be added. I will get the example for you as soon as I can.