New: Add customer note when subscribing to MailChimp list is successful or fails.
New: Add rcp_mailchimp_pro_subscribe_success action hook that triggers when subscribing a user to a MailChimp list is successful.
New: Add rcp_mailchimp_pro_subscribe_failed action hook that triggers when subscribing a user to a MailChimp list fails.
Fix: Confusing "Please enter valid API details" error message when you do have an API key entered, but just have no lists created in MailChimp.
Tweak: Reduce priority on opt-in checkbox. This ensures it's grouped with other registration checkboxes, like the Auto Renew one.
Tweak: Update plugin author name and URL.
