Fix support for Breadcrumb NavXT 5.1.1

git-svn-id: https://plugins.svn.wordpress.org/breadcrumb-navxt-multidimension-extensions/trunk@957748 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update readme to reflect change in BCN version support

git-svn-id: https://plugins.svn.wordpress.org/breadcrumb-navxt-multidimension-extensions/trunk@957752 b8457f37-d9ea-0310-8a92-e5e31aec5664