Add crossmark button if \IACR@CROSSMARKURL is defined.

[kmccurley]

If \IACR@CROSSMARKURL is defined, then it shows a crossmark button. The \IACR@CROSSMARKURL should have the format shown by the crossmark documentation

https://crossmark.crossref.org/dialog/?doi=10.5555/12345678&domain=pdf&date_stamp=2008-08-14

I plan to put the following into the main.iacrmetadata file:

\def\IACR@DOI{10.62056/aptwalk}
\def\IACR@Published{2024-02-03}
\def\IACR@CROSSMARKURL{https://crossmark.crossref.org/dialog/?doi={\IACR@DOI}\&domain=pdf\&date\_stamp={\IACR@Published}}

There are several things that we might consider changing:

1. the size of the image
2. the position of the image
3. the url can actually omit the date_stamp.

I've attached a sample:
iacrdoc.pdf

[jwbos]

Looks good, I pushed a minor change. When testing I noticed that the Received, Accepted, and Published information was displayed also for non-final versions when provided in the meta file.

[kmccurley]

In looking back at it, it was convenient to have \IACR@Received, \IACR@Revised, , \IACR@Accepted, and \IACR@Published as defaults in the class when we started, but we certainly don't need them now. They are set in publish.iacr.org as follows:

1. \IACR@Received takes the value from HotCRP, which is authenticated in the upload URL.
2. \IACR@Accepted takes the value from HotCRP, which is authenticated in the upload URL.
3. \IACR@Published is set to the compile time, which is a little optimistic.
4. \IACR@Revised is never set and I don't see any path for us to set it. I think it should be removed.
   I would prefer that we set \IACR@Received and \IACR@Accepted and \IACR@Published to \@emptyin iacrcc.cls, and get rid of \if@IACR@Received completely, and use a test \ifx\IACR@Received\@empty\else...\fi instead. The booleans don't really serve any purpose.

[jwbos]

In looking back at it, it was convenient to have \IACR@Received, \IACR@Revised, , \IACR@Accepted, and \IACR@Published as defaults in the class when we started, but we certainly don't need them now. They are set in publish.iacr.org as follows:

1. \IACR@Received takes the value from HotCRP, which is authenticated in the upload URL.
2. \IACR@Accepted takes the value from HotCRP, which is authenticated in the upload URL.
3. \IACR@Published is set to the compile time, which is a little optimistic.
4. \IACR@Revised is never set and I don't see any path for us to set it. I think it should be removed.
   I would prefer that we set \IACR@Received and \IACR@Accepted and \IACR@Published to \@emptyin iacrcc.cls, and get rid of \if@IACR@Received completely, and use a test \ifx\IACR@Received\@empty\else...\fi instead. The booleans don't really serve any purpose.

I can take this one. Will work on this later this week.

[jwbos]

Done in latest commit. Please review. 073dc9f