feat: add katex support

[jcgruenhage]

This is mostly copy-paste of getzola/even#16.

I tested it locally, works as expected.

I'm still wondering whether zola can do anything to make this less painful, as porting KaTeX rendering to every theme is quite a lot of duplication. This is okay now, but updating will be a major PITA. A solution where zola inserts these would be a lot better IMO.

[Keats]

There is getzola/zola#1073 but it doesn't seem to build on Windows

[jcgruenhage]

Ah, amazing, hadn't seen that one yet!

[jcgruenhage]

I'm still wondering whether zola can do anything to make this less painful, as porting KaTeX rendering to every theme is quite a lot of duplication. This is okay now, but updating will be a major PITA. A solution where zola inserts these would be a lot better IMO.

The generalized version of this still holds true though, if you take other client side rendering extensions, like mermaidjs for example.

[c-git]

I'm trying to add some latex to my page and would prefer not use images. I'm a bit confused what the viable options are (other than images, which is my current fall back). I see katex has a wasm option now. I don't know how long they've had that. I'm mostly asking if anyone already knows before I keep digging.