Truffle/Source Attribution: Replace direct creation of SourceSection objects with factory methods on Source; two of these greatly simplify source attribution by automatically computing either the row/column start location from a character offset or vice versa, depending on what?s made available from the parser. Minor API change on Visualizer.

// A simple interface, to allow an unknown foreign call from a class
// loaded with LOADER1 to a class loaded with LOADER2.
public interface IFace {
  public many_loader[] gen();
}