Add simple benchmark script

Change-Id: I349476e7a795cc5556060f2ee318e165c83c1890
diff --git a/Makefile.PL b/Makefile.PL
index 1467c1e..2cc7547 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -16,6 +16,8 @@
     'XML::Loy' => 0.49,
     'IO::Uncompress::Unzip' => '2.091',
     'Pod::Usage'      => 0,
+    'Dumbbench' => '0.111',
+    'DateTime' => '1.51'
   },
   PREREQ_PM => {
     'XML::CompactTree::XS'     => '0.03',