Hide internal classes from public API. Need flat package structure.

http://stackoverflow.com/questions/22967749/java-subpackaging-without-making-subpackge-classes-public
Refactored Serialized. Unified Exceptions.
Refactored ZMQWrapper to use TransferHelper. 

Makes several improvements of TransferHelper necessary:
- envelope hanlding
- TransferWrapper handles serialization
No return messages for OneWayRequests. Solves #18.