Added output when message are marked read (if ```--json```), which fixes Issue [#516] (https://github.com/vysheng/tg/issues/516#issuecomment-101710890)
Also added event field to json which will be send to terminal/main_session:
"event" = "message", "read" (message got read), "service", (events only in secret chats?)  "updates" (peer name change etc), "download" (file downloaded)