If someone issues a command like
#upgrades now Upgrades SIG https://etherpad.openstack.org/p/ffu-ptg-rocky
then make the URL a hyperlink so that viewers of the webpage can
easily jump to the etherpad to learn about the topic being discussed
and make a quick but informed decision whether it's worth them going
to that room.
To avoid duplicating the word iteration logic, we do this by extending
the existing "hashtag" helper; however this widens its scope beyond
merely formatting hashtags, so also rename the helper to reflect this.