Inline SVG math in HTML output.

It'd be super great if MultiMarkdown had an option to produce inline SVG's for its math so one doesn't have to include a JS-based math renderer on one's page.

This can be accomplished with `dvisvgm --no-fonts`, which is included with [several Tex distros](https://dvisvgm.de/Links/). If it's helpful, below is a functioning Ruby script for replacing `math` spans from MultiMarkdown HTML with inline SVGs.

```ruby
USAGE = 'Converts math in ... to inline SVG. Usage: $ ruby math_to_svg.rb file.html'

path = ARGV[0] || (STDERR.puts USAGE; exit 1)

`mkdir -p tmp`

new_html =
File.read(path).gsub(/\\\(([\s\S]*?)\\\)<\/span>/) do |match_str|
latex_str = $1.gsub("<", "<").gsub(">", ">")
latex_doc = %Q|\\documentclass{standalone}\n\\usepackage{amsmath}\n\\begin{document}\n$#{latex_str}$\n\\end{document}|

File.write("tmp/tmp.tex", latex_doc)

if system("pdflatex -output-format=dvi -interaction=nonstopmode -output-directory=tmp tmp/tmp.tex")
if system("dvisvgm --output=tmp/tmp.svg --no-fonts tmp/tmp.dvi")
File.read("tmp/tmp.svg")
else
match_str
end
else
match_str
end
end

`rm -r tmp`

File.write(path, new_html)
```

Start with the supplied math_to_svg.rb script and its pdflatex and dvisvgm workflow, then locate the existing MultiMarkdown HTML math-output entry point. The work is done when an option produces inline SVG math without a JavaScript renderer, while preserving the existing output behavior when the option is not enabled.

Written by the indexing model from the issue text.