Feature request: Image alt text

[filcuk]

This is typically implemented as: ![Alt text](URL or file path)
A title or caption would also be very useful: ![alt text](image url "image Title")

It would work alongside #493: ![alt text](image url "image Title" | resolution)
(note that above issue suggests a slightly different arrangement for alt text & resolution in comments, either is fine).

[GiantCrocodile]

Image alt text is already working but caption/title is missing it looks like, I reported something similar: #862.