Add queued message editing #10

Currently, if the user makes a typo or wants to rephrase a queued prompt, their only choice is to clear the queue and rewrite it or wait until the queue reaches that point to cancel and correct.

I see two possible solutions, whichever you think more fitting would be great to have:

• /queue:edit [ | first | last]
• /queue:edit => opens an editing menu

If pull requests are accepted, I wouldn't mind working on said feature myself and opening one for review.