[texdvd] Make the DVD iso images available for download

[Karl Berry]

Hi Daniel,

    How about making the dvd iso images available for download, 

Indeed. TeX Live has always been distributed as an .iso (among other
methods) -- https://tug.org/texlive/acquire-iso.html. It should be
straightforward to provide an .iso for the full MiKTeX distribution, too.

We imagined that there would be little use in having an .iso for
MacTeX[.pkg], but if it turns out to be useful, it would be easy to do.

Finally, we imagined that there would no real reason to keep making the
ctan snapshot.

Thanks for the note,
Karl