update markdown version

Changed `markdown.md` VERSION from "28.1 2025-02-02"
to "28.2 2025-04-28".

Updated sitemap.

Tested the above via `make www gen_status gen_sitemap timestamp` on macOS.

markdown.html

@@ -431,7 +431,7 @@
 <h2 id="ioccc-markdown-guidelines-version">IOCCC Markdown guidelines version</h2>
 </div>
 <p class="leftbar">
-These <a href="markdown.html">IOCCC markdown guidelines</a> are version <strong>28.1 2025-02-02</strong>.
+These <a href="markdown.html">IOCCC markdown guidelines</a> are version <strong>28.2 2025-04-28</strong>.
 </p>
 <p><strong>IMPORTANT</strong>: Be sure to read the <a href="next/rules.html">IOCCC rules</a> and <a href="next/guidelines.html">IOCCC
 guidelines</a>.</p>

markdown.md

@@ -7,7 +7,7 @@
 </div>
 
 <p class="leftbar">
-These [IOCCC markdown guidelines](markdown.html) are version **28.1 2025-02-02**.
+These [IOCCC markdown guidelines](markdown.html) are version **28.2 2025-04-28**.
 </p>
 
 **IMPORTANT**: Be sure to read the [IOCCC rules](next/rules.html) and [IOCCC

sitemap.xml

@@ -15490,11 +15490,11 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/markdown.html</loc>
-    <lastmod>2025-04-28T20:00:17+00:00</lastmod>
+    <lastmod>2025-04-28T20:19:21+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/markdown.md</loc>
-    <lastmod>2025-04-28T19:59:57+00:00</lastmod>
+    <lastmod>2025-04-28T20:19:11+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/news.html</loc>
@@ -15598,7 +15598,7 @@
 </url>
 <url>
     <loc>https://www.ioccc.org/status.html</loc>
-    <lastmod>2025-04-28T20:09:44+00:00</lastmod>
+    <lastmod>2025-04-28T20:19:27+00:00</lastmod>
 </url>
 <url>
     <loc>https://www.ioccc.org/status.json</loc>