This new features is available with M-p and M-n (previous/next).
It saves the last highlight viewed, meaning that if you scroll in the
buffer, M-n or M-p will take you to the next or previous hl compared to
the one before you started scrolling.
For convenience, going to the previous highlight of the first highlight
will take you to the bottom of the buffer, and going to the next
highlight of the last highlight will do *the same*.
If there are several highlights in one message, only the first line will
be considered a highlight.
