added new taxonomy for storing variations

git-svn-id: https://plugins.svn.wordpress.org/photopress-paypal-shopping-cart/trunk@857694 b8457f37-d9ea-0310-8a92-e5e31aec5664
changing tag in readme

git-svn-id: https://plugins.svn.wordpress.org/photopress-paypal-shopping-cart/trunk@857695 b8457f37-d9ea-0310-8a92-e5e31aec5664