pow method

Implementation

@override
UnitConverter pow(int exp) {
  if (exp == 0) return IdentityConverter();

  int i = exp.abs();
  final base = exp < 0 ? inverted : this;
  if (i == 1) return base;

  UnitConverter result = base;
  while (i-- > 1) {
    result = result.composeWith(base);
  }
  return result;
}