Improvement of esl.Connection.message

Fixed: missing subject argument in esl.Connection.message. Added: deliveryConfirmation argument in esl.Connection.message

I needed to make messages delivery confirmation. So, after some researh, I founded [this](https://github.com/FreeSWITCH/FreeSWITCH/commit/b8f0d11a8a32446637ff6ef3d783a0cd68bc5abf): if you set header 'blocking' in event SMS::SEND_MESSAGE, mod_sms will fire SMS::SEND_MESSAGE with delivery status in header 'Delivery-Failure'. 

If everything is ok, could you also update package in npm?