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.md

@@ -212,9 +212,9 @@ FAQ on "[obtaining and compiling the most recent mkiocccentry tools](../faq.html
 and the
 FAQ on "[how to enter the IOCCC](../quick-start.html#enter)"
 as that FAQ has important details on
-[how to register](register.html)
+[how to register](../next/register.html)
 as well as
-[how to upload your submission](submit.html) to the IOCCC.
+[how to upload your submission](../next/submit.html) to the IOCCC.
 </p>
 
 <p class="leftbar">
@@ -2577,9 +2577,9 @@ FAQs on "[obtaining, compiling, installing and using the mkiocccentry tools](../
 and the
 FAQ on "[how to enter the IOCCC](../quick-start.html#enter)"
 as that FAQ has important details on
-[how to register](register.html)
+[how to register](../next/register.html)
 as well as
-[how to upload your submission](submit.html) for the IOCCC.
+[how to upload your submission](../next/submit.html) for the IOCCC.
 </p>