Eleventy Transform: allow overriding settings on a per-image basis

[valadaptive]

I have some thumbnails that I can get away with a lower quality setting on, but also a lot of full-size images and UI screenshots that I want to look nicer. There doesn't currently appear to be a way to set things like quality on a per-image basis without using a shortcode for all my images (which is a bit annoying since I don't know how many template engines support things like named arguments, and there are a lot of image attributes I may want to add).

I could see a couple ways of implementing this: some sort of hook in the plugin settings itself that gives access to the <img> element's attributes (either in addition to transform or as an additional argument to it), or a custom eleventy:settings attribute on the element itself. Not too sure about the exact shape of either.