Improve error handling

[JSpiner]

related with #81

1. Add defaultErrorListener
   I created a default listener that only throws an OnErrorNotImplementedException if it is not set.

2. Add error handling
   Added error handling at empty handling code.

[ParkSangGwon]

Do you want change policy forced to implement ErrorListener?
As-is policy is setOnErrorListener() is optional

[JSpiner]

@ParkSangGwon
No! It does not force to implement ErrorListener.
As we discussed,

Library단에서 OnErrorListener를 set()해주도록 제공해주고 만약 구현되어있다면 해당 listener에게 알려주고
그렇지 않다면 throw로 에러를 발생시키는 방식으로 하면 좋을것 같습니다.

If ErrorListener is implemented, just call it.
If ErrorListener is not implemented and error occurs, it throws error by default listener.

[JSpiner]

OnErrorNotImplementedException is thrown if an error has occurred and an ErrorListener has not been implemented.

[ParkSangGwon]

@JSpiner I forgot...
Then please add setOnErrorListener() in sample code

[JSpiner]

That's good.
I'll add some sample code and push changes!
Thanks.

[ParkSangGwon]

@JSpiner
Please add sample code.

[JSpiner]

@ParkSangGwon
can you review it?

[ParkSangGwon]

@JSpiner
Sorry, I can not remember this comment.

Library단에서 OnErrorListener를 set()해주도록 제공해주고 만약 구현되어있다면 해당 listener에게 알려주고
그렇지 않다면 throw로 에러를 발생시키는 방식으로 하면 좋을것 같습니다.

Please make optional setOnErrorListener().
This mean even If user didn't implement error listener, error don't occur