Add ability to show notifications for messages in a channel you recently posted

[3v1n0]

Say you're in a channel, you've just wrote something and someone replies you back without mentioning you. But you tabbed out.

This is a quite common scenario cause people expect you to be there if they mention you just after you wrote.

So basically... Add an option to notify all the messages after you wrote something in a buffer within a timeout (I'd say set to 3 seconds as default...).