stop-and-wait

A java implementation of this simple ARQ mechanism.

This strategy cover 3 different problems.

1. Lost Data.
2. Lost Acknowledgement.
3. Delayed Acknowledgement/Data.

TODO

1. create a class for sender and receiver.
2. improve the marshalling and unmarshalling of data, using only bytes, not objects.
3. improve the code to be more readable and clean.
4. add a checksum strategy.