Update to 1.3.8; file structure changes, feature adds, bug fixes

git-svn-id: https://plugins.svn.wordpress.org/wp-accessibility/trunk@994879 b8457f37-d9ea-0310-8a92-e5e31aec5664
Promote 1.3.8 to stable tag

git-svn-id: https://plugins.svn.wordpress.org/wp-accessibility/trunk@994881 b8457f37-d9ea-0310-8a92-e5e31aec5664