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.

bin/md2html.cfg

@@ -565,6 +565,42 @@ years.md
 	-D
 	../
 
+# Year level rules
+
+[12][0-9][0-9][0-9]/rules.md
+	-H
+	navbar=empty
+	-o
+	bin/subst.default.sh
+	-s
+        TITLE=The International Obfuscated C Code Contest
+	-s
+	DESCRIPTION=Archive of IOCCC Rules
+	-s
+	KEYWORDS=IOCCC, rules, Rules
+	-s
+	HEADER_2=Archive of IOCCC Rules
+	-D
+	../
+
+# Year level guidelines
+
+[12][0-9][0-9][0-9]/guidelines.md
+	-H
+	navbar=empty
+	-o
+	bin/subst.default.sh
+	-s
+        TITLE=The International Obfuscated C Code Contest
+	-s
+	DESCRIPTION=Archive of IOCCC Guidelines
+	-s
+	KEYWORDS=IOCCC, guidelines, Guidelines
+	-s
+	HEADER_2=Archive of IOCCC Guidelines
+	-D
+	../
+
 # Unless matched above, default process all entry README.md files
 
 [12][0-9][0-9][0-9]/*/README.md