allow for year level archive of rules and guidelines

Adjusted `bin/md2html.cfg` to allow for the creation of year level
archive of the rules and guidelines that were in effect when the given
year's content opened for submissions.

We improved `bin/gen-year-index.sh` so that if there exists
a `YYYY/rules.md` rules archive, then `YYYY/rules.html`
will be created.

We improved `bin/gen-year-index.sh` so that if there exists
a `YYYY/guidelines.md` rules archive, then `YYYY/guidelines.html`
will be created.

Changed `bin/gen-year-index.sh` VERSION from "2.0.0 2025-03-13"
to "2.1.0 2025-07-05".

Adjusted `next/rules.md` and `next/guidelines.md` so that when they are
copied as archived copies of rules and guidelines under a YYYY directory,
the internal links do not break.  There are **NO** changes to the readable
contents of the rules and guidelines, only some changes to a few internal links.

Updated `1992/buzzard.2/index.html, `1993/rince/index.html`, and
`2012/omoikane/index.html that were modified by recent commits.

Rebuild sitemap due to the changes above.

Ran `make www` to test and perform the above.

next/guidelines.html

@@ -588,9 +588,9 @@ FAQ on “<a href="../faq.html#mkiocccentry">obtaining and compiling the most re
 and the
 FAQ on “<a href="../quick-start.html#enter">how to enter the IOCCC</a>”
 as that FAQ has important details on
-<a href="register.html">how to register</a>
+<a href="../next/register.html">how to register</a>
 as well as
-<a href="submit.html">how to upload your submission</a> to the IOCCC.
+<a href="../next/submit.html">how to upload your submission</a> to the IOCCC.
 </p>
 <p class="leftbar">
 See also the
@@ -2496,9 +2496,9 @@ FAQs on “<a href="../faq.html#mkiocccentry">obtaining, compiling, installing a
 and the
 FAQ on “<a href="../quick-start.html#enter">how to enter the IOCCC</a>”
 as that FAQ has important details on
-<a href="register.html">how to register</a>
+<a href="../next/register.html">how to register</a>
 as well as
-<a href="submit.html">how to upload your submission</a> for the IOCCC.
+<a href="../next/submit.html">how to upload your submission</a> for the IOCCC.
 </p>
 <hr style="width:10%;text-align:left;margin-left:0">
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