Generate an image set by multiple images in a row

[fluffy-critter]

Expected Behavior

The following Markdown should generate a single image set:

![a cat](cat.jpg)
![another cat](cat2.jpg)
![not a cat](dog.jpg)

Current Behavior

Those images are all treated as separate inline images (probably). There is currently no means of specifying per-image alt text, either.

Context

Specifying alt text on image set images is annoying, and using more standard syntax for images that better-enables the use of alt text would be preferable to the current mechanism.

Also, the Publ-specific Markdown for image sets probably isn't a great choice in general either.

Obvious question, though: how does it interact when there's multiple images with separate configurations, especially regarding caption="..."?