Validation

[Mikhail42]

The FHIR types definition contains rules. E.g., Code should not be white space. I think we can add validation in class constructor. Second, some classes have very many constructor's params. I thinks they should be with predefinition values in same cases. Element, on other case, can't has all params. I think, we can use a methods to get or set specific type value.

Sorry for my English, I don't want to use translator.
Thanks for repository.