conversion:fromCol

https://github.com/timrdf/csv2rdf4lod-automation/issues/339

      conversion:enhance [
         conversion:fromCol        2;
         conversion:toCol          4;
         a qb:Observation;
      ];

is equivalent to:

      conversion:enhance [
         ov:csvCol 2, 3, 4;
         a qb:Observation;
      ];