This indents all but the first line of multi-line annotations for
individual enum variants with four spaces so that pandoc will
recognize everything as belonging to the same list item.
Since that introduces `<p>` tags for some list items, I've gone ahead
and inserted blank lines after each list item so that consistently
get `<p>` tags for all `<li>`s documenting variants. It's a bit less
compact now but still tolerable, I think.