Make all links bold

This does mean that in some cases there is now redundant markdown '**'s
to make the links bold but those can be removed as they are discovered -
or not.

ioccc.css

@@ -420,6 +420,7 @@ a {
     outline-color: transparent;
     text-decoration: none;
     padding: 2px 1px 0;
+    font-weight: bold;
 }
 
 a:link {