turn off app cache, print generation date at bottom

lib/dartdoc/dartdoc.dart

Index: lib/dartdoc/dartdoc.dart
diff --git a/lib/dartdoc/dartdoc.dart b/lib/dartdoc/dartdoc.dart
index b860a94fbacf5bc11b413c990c0c171dd9781ce0..738026ea786af11ef65946c4c1a1e7a3f70fea7a 100644
--- a/lib/dartdoc/dartdoc.dart
+++ b/lib/dartdoc/dartdoc.dart
@@ -461,7 +461,10 @@ class Dartdoc {
         <div class="clear"></div>
         </div>
         ${preFooterText}
-        <div class="footer">$footerText</div>
+        <div class="footer">
+          <p>This page generated at ${new Date.now()}</p>
+          <div>$footerText</div>
+        </div>
         <script async src="${relativePath('$clientScript.js')}"></script>
         </body></html>
         ''');