I took the list from https://github.com/FortAwesome/Font-Awesome/wiki/Upgrading-from-3.2.1-to-4#new-icon-names

I think the `'sort-up' => 'sort-desc'` is a mistake on the wiki page.

I agree we can create an `asciidoctor-font-awesome-compat.css` in `data/stylesheets/` and add it like [CodeRay](https://github.com/asciidoctor/asciidoctor/blob/master/lib/asciidoctor/converter/html5.rb#L77). I just need a regexp to map icon name with UTF-8 character :smile: