support @mention syntax for user assignment or mentions
I've found that if the first word is followed by a ":" (e.g. "Aymeric:"), it is rendered differently. I would like the same treatment for words with the mention syntax (e.g. "@Aymeric"). That is the more widespread notation for mentions.
This may be useful for indicating task assignment among users, but is useful even otherwise, because even when drawing up a personal task list, many of those tasks involve interacting with other people, and distinguishing them would help with organization.