Checking in changes prior to tagging of version 0.21.

Changelog diff is:

diff --git a/perl/Changes b/perl/Changes
index dc3dd5c..5d5a5e2 100644
--- a/perl/Changes
+++ b/perl/Changes
@@ -1,3 +1,8 @@
+0.21
+
+    - doc enhancment
+    - micro performance tuning.
+
 0.20

     - first production ready release with PP driver.

perl/lib/Data/MessagePack.pm

@@ -3,7 +3,7 @@ use strict;
 use warnings;
 use 5.008001;
 
-our $VERSION = '0.20';
+our $VERSION = '0.21';
 our $PreferInteger = 0;
 
 our $true  = do { bless \(my $dummy = 1), "Data::MessagePack::Boolean" };