Suggestion/Request: dither effect options for user-defined palette and Bayer ordered dithering

Equivalent example using ImageMagick (where `-ordered-dither` might be o2x2, o4x4, or o8x8):

```bash
magick input.png -remap palette.png -ordered-dither o4x4 output.png
```

(Edited to remove link to the `image-effects` crate, which looked promising but does not actually seem to have a functional ordered dither implementation.)