Get rid of a couple of copies of the CC0 text. Add header comment to
CC0 files to remind people editing them what the terms are. Also add
some missing XML headers. The header comments in layouts won't bloat
the binary - they get stripped out before compressing, same as any other
comments.
out of whatsnew: the disk dumps do not come from original media, but given that no more program disks ever appeared in the past two years and that even the website which originally hosted these disks disappeared, it is definitely worth documenting them before they get lost forever...