visit the next image file and the previous image file in the same
directory, respectively.
++++
*** New commands to show specific frames of multi-frame images.
`f' (`image-next-frame') and `b' (`image-previous-frame') visit the
next or previous frame. `F' (`image-goto-frame') shows a specific frame.
++++
*** New commands to speed up, slow down, or reverse animation.
+`a +' (`image-increase-speed') and `a -' (`image-decrease-speed') to
+speed up and slow down the animation. `a r' (`image-reverse-speed')
+to reverse it and `a 0' (`image-reset-speed') to reset it.
+
---
*** The command `image-mode-fit-frame' deletes other windows.
When toggling, it restores the frame's previous window configuration.