[Feature requests] Scale smallest side to size + only enlarge or shrink

[Jolar]

It would be nice to have an option for scaling images in respect to just the smallest side.

And also, it would be very nice to have the option to skip pictures that already are larger or smaller than what you're scaling to.

Example:
A.gif 500x180px
B.gif 220x400px
C.gif 500x320px

gifsicle --batch --resize-smallside 256 --enlargeonly -i *.gif

Would resize A to 712x256, B to 256x466 and skip C. --shrinkonly would of course instead only affect C and resize to 400x256.

I'd use this because of Google photos - it only automatically backups images with a smallest side of 256 pixels or larger, and I have a humongous amount of animated gifs I'd like to backup, but many of them are too small, and there's hundreds if not thousands of gifs with different resolutions in various folders.