Provide support for pandoc-crossref figures and subfigures

[p3palazzo]

Hi, I created a fork of your theme (also available on RubyGems) that provides some support for figures and subfigures generated by pandoc-crossref, among other things. As far as I tested it breaks nothing in your theme. Let me know you are interested in these features so I can open a pull request.

Edit: I also added a dark mode and accommodations for reveal.js code. You will probably not find appropriate to merge these into your project. I can commit only a subset of these features to create the PR.