Update to Content API v2

git-svn-id: https://plugins.svn.wordpress.org/guardian-news-headlines/trunk@1011610 b8457f37-d9ea-0310-8a92-e5e31aec5664
tagging version 0.5.3

git-svn-id: https://plugins.svn.wordpress.org/guardian-news-headlines/trunk@1011616 b8457f37-d9ea-0310-8a92-e5e31aec5664