[Feature Request] add unread count to "New Posts" indicator

[danguyf]

When refreshing a feed, when posts are loaded in place, so to speak, e.g. without resetting the view to the newest post, a "New Posts ^^^" indicator appears at the top. I think it would be useful to have the number of new posts added to this indicator.

That bit is trivial. I expect the trickier bit is having that number count down as you scroll up and view posts.