* Added IsEcho in Message which is indicator of own messages
* Added QuickReply in Message for sending of quick reply buttons with message
* Added mux parameter in Messenger constructor. It is useful when single go app processes the several bots
* Added Messenger.SenderAction which allows to show writing and reading status
* Added Messenger.GreetingSetting and Messenger.CallToActionsSetting which allow to set the bot settings
* Fixed bug with nil returning instead of error object
