Write a tutorial about the generation of HL7 message classes for the Hapi validation.

This tutorial is for the IHE team.
In some cases, when we use EVSClient tool to validate HL7v2 messages, it appears that the validation result is FAILED in spite of we are certain that this validation result should be PASSED.
This problem appears when the message structure defined by IHE is different from the initial message structure defined by HL7. The solution is to generate the message classes, used by Hapi for the validation.
It explain how generate generate this classes and how to test it.

Need to share the HapiClassGenerator and the HapiValidatorTest project in the forge.