There's a few more cases that needs proper quoting for Sphinx. Asterisks
and ticks at the start of words, as well as underscores at the end of
symbols, even when they have trailing escaped characters.

We should really find a way to robustly escape these things when
generating them.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <!8243>