Allow screenshot bundling

[razzeee]

It would be useful to bundle screenshots e.g.

<picture>
	<pic>
		<image>url1_light</image>
	</pic>

	<pic>
		<image>url1_dark</image>
	</pic>

	<caption>Main screen of application</caption>
</picture>

This would be helpful in the web, to be able to create https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/picture elements according to light/dark styles used and knowing which images to show/don't show.