Feature Request: distinguish numbered lists and example lists in HTML

[alexklapheke]

As of the fixing of #1902, there is no way to distinguish example numbering in HTML output from ordinary numbered lists. It would be nice to have something like class="example" on the former so that these can be styled differently.

I understand I can just wrap the example lists in <div> blocks (#2408), but this seems like a natural addition given that pandoc's syntax treats the two list types as categorically different.