Update compatibility to WordPress 4.0.

git-svn-id: https://plugins.svn.wordpress.org/download-html-tinymce-button/trunk@981021 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update compatibility to WordPress 4.0.

git-svn-id: https://plugins.svn.wordpress.org/download-html-tinymce-button/trunk@981023 b8457f37-d9ea-0310-8a92-e5e31aec5664
Add update description.

git-svn-id: https://plugins.svn.wordpress.org/download-html-tinymce-button/trunk@981027 b8457f37-d9ea-0310-8a92-e5e31aec5664