Double opt-in

[christopherowen]

Please add a method to enable double opt-in.

according to the documentation at http://developer.mailchimp.com/documentation/mailchimp/guides/manage-subscribers-with-the-mailchimp-api/

This is achieved by sending 'pending' instead of 'subscribed' during the mailchimp API call.

[lnbogen]

I second @christopherowen's request.