Confusion parameter options in Dictionarizer, ColumnCopier etc. #189

The following transform can operate on multiple columns either by using tuple [(input, output), (input2,output2), ... , (input_n,output_n)] or string array [col1,col2....coln]

There is no error for the following option. Both work fine. However, no.1 is actually not correct. Can we simplify it? or at least flag error because "Label" column is not yet there in the pipeline.

1. pipeline.Add(new Dictionarizer("Area", "Label"));
2. pipeline.Add(new Dictionarizer( ("Area", "Label") ));