Added 'callback' option

git-svn-id: https://plugins.svn.wordpress.org/jumplead/trunk@1010778 b8457f37-d9ea-0310-8a92-e5e31aec5664
Tagged 3.0.7

git-svn-id: https://plugins.svn.wordpress.org/jumplead/trunk@1010779 b8457f37-d9ea-0310-8a92-e5e31aec5664