Notification system

[benharri]

BBJ should send mails to a mentioned or replied-to user when a new message is posted.

We can have a look at message_feed or the point where a >>NUM gets parsed to figure out the author of the the in-reply-to post.

[MineRobber9000]

I think this can be tied into #8. (As in, you can subscribe to feeds and get an email when they update.)

This should be opt-in, if implemented at all. Especially since you need an email to send the notifications to.

[benharri]

Could also be configured to use the local mail on a system as well (configurable of course).