def collect_matching_lines(marc_record)
      results = []
      self.each_matching_line(marc_record) do |field, spec, extractor|
        results.concat [yield(field, spec, extractor)].flatten
      end
      return results
    end
def collect_matching_lines(marc_record)
      results = []
      self.each_matching_line(marc_record) do |field, spec, extractor|
        results.concat [yield(field, spec, extractor)].flatten
      end
      return results
    end
line each_matching_line, takes a block to process each matching line,
 but collects results of block into an array -- flattens any subarrays for you!

 Useful for re-use of this class for custom processing

 yields the MARC Field, the MarcExtractor::Spec object, the MarcExtractor object.