MathJax 3 support

[voidbert]

The proposal

Currently, haddock uses MathJax 2.7. Due to new features, new packages, etc., I believe some users would be interested in the option of using MathJax 3.

I opened this issue to see if someone would be interested in this feature, and to discuss how it could be implemented.

Inherent problem and fix

MathJax 3 introduces some API breaking changes. More than breaking configuration files (which could easily be fixed from haddock's end), this breaks some existing formulas. Therefore, it may be a good idea to let users choose between the older and newer version.

I am aware that a custom MathJax URL can be provided (--mathjax [url]). However, due to the different configuration files needed, I suggest introducing a new command-line option (like --mathjax3 [url]).

In the future

If people are interested in this feature, and it ends up being implemented, a way to integrate it with cabal would be needed.