code: func DescByFieldIndex(slice interface{}, index []int) {
  	New(slice, FieldByIndexGetter(index), Descending).Sort()
  }
docs: // Sort a slice in descending order by a list of nested field indices, e.g. 1, 2,
  // 3 to sort by the third field from the struct in the second field of the struct
  // in the first field of each struct in the slice.