Add alt url to Anders Gavare

This is specific to their winning entry (which is actually referred to
in the index.html file).

author/Anders_Gavare.json

@@ -7,7 +7,7 @@
     "location_code" : "SE",
     "email" : "gavare@gmail.com",
     "url" : "https://gavare.se",
-    "alt_url" : null,
+    "alt_url" : "https://gavare.se/ioccc/ioccc_gavare.c.html",
     "deprecated_twitter_handle" : null,
     "mastodon" : null,
     "mastodon_url" : null,

authors.html

@@ -1687,6 +1687,8 @@ Location: <a class="normal" href="location.html#SE">SE</a> - <em>Sweden</em>
 <br>
 URL: <a class="normal" href="https://gavare.se">https://gavare.se</a>
 <br>
+Alternate URL: <a class="normal" href="https://gavare.se/ioccc/ioccc_gavare.c.html">https://gavare.se/ioccc/ioccc_gavare.c.html</a>
+<br>
 author_handle: <a class="normal" href="https://github.com/ioccc-src/temp-test-ioccc/blob/master/author/Anders_Gavare.json">Anders_Gavare</a>
 <p>
 </p>