Fully specify custom type

[bendbennett]

Within the Generator there is currently no way to fully override custom types for lists, maps, objects and sets. For instance:

	case e.List != nil:
		if e.List.CustomType != nil {
			return fmt.Sprintf("%s{\nElemType: %s,\n}", e.List.CustomType.Type, GetElementType(e.List.ElementType))

Once this has been addressed in the specification, then the code handling custom types for list, map, object and set will need updating in the generator.