[wlug] PNG Spec, 3rd Edition, Is Out

There is has been a major update to the specification for the PNG (“Portable Network Graphics”) file-format spec <https://www.programmax.net/articles/png-is-back/>, 20 years on from the previous edition. New features include support for high-dynamic-range colour gamuts, using a new metadata entry type that is much more compact than a full embedded ICC colour profile, and the official acceptance of the APNG format for animating a sequence of images within a single PNG file.