Added Continue Sopping button and fix missing variables

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-direct-checkout/trunk@944494 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated readme 

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-direct-checkout/trunk@944496 b8457f37-d9ea-0310-8a92-e5e31aec5664