latex (remark-math) support

[wwsalmon]

any chance latex support ($ and $$) could be added? it's not strictly markdown but I imagine it's a pretty common use case and https://github.com/inokawa/remark-slate-transformer supports it based on https://github.com/Rokt33r/remark-math plug-in for remark.

should be pretty easy to implement, happy to put in a PR for this if you're willing to merge

[hanford]

Rather than specifically adding support for remark-math I wonder if remark-slate could expose an escape hatch for any type of customization