We also explicitly check for None, instead of assuming truth value,
this allows a user to pass "" as a username if they *really* want to
shoot themselves in the foot.

The changed lines are interpreted as markdown links but they should not
be. With `` we force markdown to avoid parsing those as links

Some errors that I either created or did not see before the changes
happened.

This brings us closer to having a test of mdlintall that's happy -- but
not 100%: there's still errors about checkboxes that look like links and
confuses mdl

After one too many pipeline failures due to old spell-checking
mistakes, I decided to own up to my stuff and spell check
everything. I actually ran:

     codespell --interactive 3 --write-changes *

And dealt with *almost* all the errors, except stuff in old/ which
I'll remove shortly.

When an error comes up now, it is new and should be fixed.