Add confirmation message to /tell responder

Acknowledged, this breaks the Rule of Silence.  Our team considered doing so a lesser-evil to messages never being delivered because the sender could not know that Hubot had not seen the command. 

I'll let the keepers of the repo determine if they agree enough to merge!

Author: BFGeorge9000

src/scripts/tell.coffee

@@ -26,6 +26,7 @@ module.exports = (robot) ->
        localstorage[room][username] += tellmessage
      else
        localstorage[room][username] = tellmessage
+     msg.send "Ok, I'll tell #{username} you said '#{msg.match[2]}'."
      return
 
    # When a user enters, check if someone left them a message