Change InternalParsedDatatype to a sealed trait
Resolve type names to Type instances
Introduce Parsed Datatype that translates strings to types. Update builder
ServiceDescriptionValidator now compiles
First pass at compiling code w/ union types
Update specs: TypeInstance => ParsedDatatype
ParsedDatatype => Datatype. InternalParsedDatatype => InternalDatatype
Update tests
Update validation for maps
Update spec