Checking in changes prior to tagging of version 0.20.

Changelog diff is:

diff --git a/Changes b/Changes
index 711b176..8e764f3 100644
--- a/Changes
+++ b/Changes
@@ -1,5 +1,7 @@
 Revision history for Perl extension CGI::Header.

+0.20  Feb 24th, 2013
+
   - Add "REQUIRED METHODS" to CGI::Header::PSGI's POD

 0.19  Feb 11th, 2013