Updated to version 3.0

git-svn-id: https://plugins.svn.wordpress.org/three-column-screen-layout/trunk@1030593 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme

git-svn-id: https://plugins.svn.wordpress.org/three-column-screen-layout/trunk@1030597 b8457f37-d9ea-0310-8a92-e5e31aec5664