Add slash to href for directories (#17)

This allows client side parsers to decide when a link is a directory.

This is needed for example in the rclone http backend.

https://rclone.org/http/

darkhttpd.c

@@ -1987,6 +1987,8 @@ static void generate_dir_listing(struct connection *conn, const char *path,
 
         append(listing, "<a href=\"");
         append(listing, safe_url);
+        if (list[i]->is_dir)
+            append(listing, "/");
         append(listing, "\">");
         append_escaped(listing, list[i]->name);
         append(listing, "</a>");