* add json omitempty on button Title field
Share Button only allows the Type field to be presented in the serialized data. Otherwise, you got facebook error:
"Facebook error : (#100) Param [elements][0][buttons][0][title] must be a non-empty UTF-8 encoded string"
* add attachement to senddata
* changes after pull request reviews
* Sending back the error message of Facebook as an error for some function calls
* Adding error handling for other function calls
* Private function to parse Facebook's response
* Handling errors for ProfileByID function
* 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
* Added Read message support
Delivered message suppport already existed but was commented as
indicating that a message was read by a user. As of the 1 July
2016 API release this isn't true, there is another event. This
commit adds read event support and corrects the description of
delivered events. Also added to the example bot.
* go fmt
* Added new profile fields from July 1st API update
* gofmt
