render: Latex support

[alixander]

the language tag latex and tex will now render LaTeX (or rather, the MathJax flavor of it)

Docs: terrastruct/d2-docs#15

closes #135

[ejulio-ts]

Edges are handled

a: |latex
x = \\frac{1}{2}
|

b: |latex
e = mc^2
|

a -> b: |latex
e = mc^2
|

If we're not going to handle them, we should show an error
If we're going to handle it in another PR, totally fine

I'm used to having latex inside markdown with $$ tags mathjax, but it doesn't seem we support it right now. I get that t it is probably out of scope for this PR, so just letting you know inc are you want to open an issue

[ejulio-ts]

Don't you need to add some NOTICE for mathjax?

[alixander]

Don't you need to add some NOTICE for mathjax?

even better -- the attribution is on the file itself (top)

[nhooyr]

nice