Fixes #7 . Emails not showing in exception

[huglester]

Now the exception is showing list of emails, like:

One or more email addresses did not pass validation: "trovster", "trovster2", "" Example code:

        $email = \Email::forge();
        $email->subject('test');
        $email->html_body('body');
        $email->from('fuel');
        $email->to('trovster', 'Trevor');
        $email->to('trovster2', 'Trevor2');
        $email->to('', '');
        $email->priority(\Email::P_HIGH);
        $email->send();

[frankdejonge]

Had some comments over on irc, waiting for that.

[frankdejonge]

I fixed it myself here: https://github.com/fuel/email/commit/7de143e4a1e129af48892acd974bb35cd935962b