`MessageData` is useful when iterating through messages

[azymnis]

When iterating through all messages in a topic or for a given me, there seems to be no way to get the message timestamp. This seems to be a member of MessageData. Any way we could have access to that in the MessageHandler?

[pjreed]

This would be useful, although digging into the code a bit, it will take a little bit of work to actually get that data available in the MessageHandler. I'll look into adding that.

[lukehutch]

@azymnis see #45, I posted some code there that will get the header timestamp for you while iterating through all messages on a given topic or list of topics.