added support for Post Title, Post Content and Post Excerpt fields
fixed textareas not rendering field values in form editor

git-svn-id: https://plugins.svn.wordpress.org/gravityforms-html5-placeholders/trunk@975345 b8457f37-d9ea-0310-8a92-e5e31aec5664
fixing readme.txt

git-svn-id: https://plugins.svn.wordpress.org/gravityforms-html5-placeholders/trunk@975346 b8457f37-d9ea-0310-8a92-e5e31aec5664