Return timestamp in sendMessage
Return timestamp in sendMessage

Send back Facebook's message timestamp in the sendMessage endpoint. I think this is necessary because Facebook's timestamps are different than my local machines'. For example, when I receive a message (with `listen()`), my Date.now() is 15 seconds off from the message's timestamp that I received from Facebook. This causes issues when users send/receive messages in a short amount of time. Using Facebook's timestamps everywhere should resolve the timestamp discrepancies I'm seeing.

Side note: is there a reason the whole message object isn't sent back?
GAMELASTER/facebook-chat-api,noodle-learns-programming/facebook-chat-api,ravkr/facebook-chat-api,tpphu/facebook-chat-api,Schmavery/facebook-chat-api,AdamBurgess/facebook-chat-api