function tipUser(bytes32 _username, bytes32 _commentId, bool _reply) public payable {
        
        tips[msg.sender][_username] += msg.value;
        
        balances[_username] += msg.value;
        
        lastTip[msg.sender][_username] = now; 
        
        UserTipped(msg.sender, _username, msg.value, _commentId, _reply);

        sendTip(_username, msg.value);
    }