version bump, minor improvements and bug fixes

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@877369 b8457f37-d9ea-0310-8a92-e5e31aec5664
readme update

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@877372 b8457f37-d9ea-0310-8a92-e5e31aec5664