[feature request] Have unread entries preceded by some context

When I enter a room with unread items, it would be nice to have a little context from previous read items in that room, e.g. the last few lines (maybe using the value of `next-screen-context-lines`, say).

Further, on a high resolution display, the line indicating where new unread items start, which is the top line of pixels in the window, is not really visible. Having it clearly visible would provide a useful visual cue as to when ement has found all unread items, avoiding trying to scroll prematurely.

Thank you!