Bootstrap typography in blog needs a Pandoc filter

[dunnl]

Issue for my own reference. Bootstrap won't always format things unless they are explicitly tagged with the right classes. An example would be blockquotes, which require a class=blockquote attribute: https://getbootstrap.com/docs/4.0/content/typography/

This isn't a problem for the HTML parts but it is a problem for the blog. We need a Pandoc filter to traverse over Pandoc AST and add classes where necessary. I have some code for this in my own website that I can adapt.