Checking in changes prior to tagging of version 0.40.

Changelog diff is:

diff --git a/Changes b/Changes
index 9ee1b73..479121f 100644
--- a/Changes
+++ b/Changes
@@ -1,5 +1,7 @@
 Revision history for Perl extension CGI::Header.

+0.40  Apr 7th, 2013
+
   - field_names() is obsolete and will be removed in 0.41
   - Add as_hashref(). get() and exists() will be replaced with this method: