Refactoring streams and fixin various bugs

Src/Data/Myc.Data.Value.pas

@@ -333,7 +333,12 @@ end;
 function TDataValue.AsScalarRecord: IKeywordMapping<TScalar>;
 begin
     if (FKind <> vkScalarRecord) then
-        raise EInvalidCast.Create('Cannot read value as Record.');
+    begin
+        if (FKind = vkRecord) then
+            raise EInvalidCast.Create('Scalar record expected.')
+        else
+            raise EInvalidCast.Create('Cannot read value as Record.');
+    end;
     Result := IKeywordMapping<TScalar>(FInterface);
 end;