Code and file structure overhaul

git-svn-id: https://plugins.svn.wordpress.org/post-list-featured-image/branches/0.5.0@961043 b8457f37-d9ea-0310-8a92-e5e31aec5664
changed: code and file structure

git-svn-id: https://plugins.svn.wordpress.org/post-list-featured-image/branches/0.5.0@961045 b8457f37-d9ea-0310-8a92-e5e31aec5664
changed: code and file structure
added: [featured_img] shortcode

git-svn-id: https://plugins.svn.wordpress.org/post-list-featured-image/trunk@961052 b8457f37-d9ea-0310-8a92-e5e31aec5664