code: public static LongColumn indexColumn(final String columnName, final int size, final int startsWith) {
          final LongColumn indexColumn = LongColumn.create(columnName, size);
          for (int i = 0; i < size; i++) {
              indexColumn.append(i + startsWith);
          }
          return indexColumn;
      }
docs: Returns a new numeric column initialized with the given name and size. The values in the column are
  integers beginning at startsWith and continuing through size (exclusive), monotonically increasing by 1
  TODO consider a generic fill function including steps or random samples from various distributions