Replace <sup> and <sub> where we can

[wbamberg]

Markdown doesn't provide a syntax for the <sup> and <sub> elements. In #4578 we decided that we would use HTML for these elements when we have to, and replace them with something equivalent where we can.

The "something equivalent" includes:

• use caret "^" for exponentiation
• use words like "first" instead of 1^st
• don't mark up footnotes with <sup>

See https://developer.mozilla.org/en-US/docs/MDN/Contribute/Markdown_in_MDN#superscript_and_subscript.

This bug is to give us a place where we can remove the use of these elements where we can.

[sideshowbarker]

@wbamberg Closing this, as it seems we have this resolved. But of course feel free to reopen if I’m wrong

[wbamberg]

I think we are good :).