Changes for version 0.03
- Fixed bug where receivePub croaked with 'OK'
- xs_publish() now returns array of (status, message handle)
- added xs_getMsgStatus() to check status of a given message
- publish() now takes an optional callback function and argument which is invoked when a QoS 1 or 2 message is delivered This is primarily so that if your messages are already locally queued, you can publish at QOS 1 without having to write them again to the persistence layer. You wait for successful delivery and then delete them from your own queue when done.