Changing shortcode to use a dash instead of underscore

git-svn-id: https://plugins.svn.wordpress.org/second-street-promotion/trunk@1052888 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updating attribution

git-svn-id: https://plugins.svn.wordpress.org/second-street-promotion/trunk@1052890 b8457f37-d9ea-0310-8a92-e5e31aec5664