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.

sitemap.xml

@@ -2346,7 +2346,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/1992/buzzard.2/index.html</loc>
-    <lastmod>2025-07-02T22:55:11+00:00</lastmod>
+    <lastmod>2025-07-06T04:09:17+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/1992/buzzard.2/Makefile</loc>
@@ -2966,7 +2966,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/1993/rince/index.html</loc>
-    <lastmod>2025-07-02T22:55:11+00:00</lastmod>
+    <lastmod>2025-07-06T04:10:06+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/1993/rince/Makefile</loc>
@@ -9142,7 +9142,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/2012/omoikane/index.html</loc>
-    <lastmod>2025-07-02T22:55:11+00:00</lastmod>
+    <lastmod>2025-07-06T04:17:26+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/2012/omoikane/Makefile</loc>
@@ -15086,7 +15086,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/authors.html</loc>
-    <lastmod>2025-05-18T11:28:49+00:00</lastmod>
+    <lastmod>2025-07-06T03:41:26+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/author/Sjoerd_Mullender.json</loc>
@@ -15278,7 +15278,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/bin/gen-year-index.sh</loc>
-    <lastmod>2025-04-16T20:59:19+00:00</lastmod>
+    <lastmod>2025-07-06T03:33:13+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/bin/gen-years.sh</loc>
@@ -15318,7 +15318,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/bin/md2html.cfg</loc>
-    <lastmod>2025-04-16T20:59:19+00:00</lastmod>
+    <lastmod>2025-07-06T03:32:49+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/bin/md2html.sh</loc>
@@ -15486,11 +15486,11 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/location.html</loc>
-    <lastmod>2025-05-18T11:30:03+00:00</lastmod>
+    <lastmod>2025-07-06T03:43:19+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/Makefile</loc>
-    <lastmod>2025-06-17T02:18:34+00:00</lastmod>
+    <lastmod>2025-07-06T04:08:33+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/markdown.html</loc>
@@ -15510,11 +15510,11 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/next/guidelines.html</loc>
-    <lastmod>2025-06-05T06:45:56+00:00</lastmod>
+    <lastmod>2025-07-06T03:49:51+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/next/guidelines.md</loc>
-    <lastmod>2025-06-05T06:45:55+00:00</lastmod>
+    <lastmod>2025-07-06T03:49:21+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/next/index.html</loc>
@@ -15550,11 +15550,11 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/next/rules.html</loc>
-    <lastmod>2025-06-05T06:45:57+00:00</lastmod>
+    <lastmod>2025-07-06T03:49:52+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/next/rules.md</loc>
-    <lastmod>2025-06-05T06:45:55+00:00</lastmod>
+    <lastmod>2025-07-06T03:48:50+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/next/submit.html</loc>
@@ -15602,7 +15602,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/status.html</loc>
-    <lastmod>2025-07-02T22:42:40+00:00</lastmod>
+    <lastmod>2025-07-06T04:21:57+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/status.json</loc>