Add upgrade notice for 0.4.1 before making it current stable version

git-svn-id: https://plugins.svn.wordpress.org/post-content-shortcodes/trunk@1018775 b8457f37-d9ea-0310-8a92-e5e31aec5664
Mark new stable version (0.4.1) in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/post-content-shortcodes/trunk@1018779 b8457f37-d9ea-0310-8a92-e5e31aec5664