Add validation.
Merge branch 'develop'
Checking in changes prior to tagging of version 0.06.

Changelog diff is:

diff --git a/Changes b/Changes
index cdcc8e4..e877f2c 100644
--- a/Changes
+++ b/Changes
@@ -2,6 +2,10 @@ Revision history for Perl extension Array-PrintCols-EastAsian

 {{$NEXT}}

+0.06 2013-12-28T05:39:16Z
+
+    - Add width validation for pretty_print_cols().
+
 0.05 2013-12-25T09:27:14Z

     - Fix README.md.