code: private static String generateAntiparallel(PolymerNotation polymer)
  			throws HELM2HandledException, RNAUtilsException, ChemistryException {
  		return generateComplement(polymer).reverse().toString();
  	}
docs: method to generate the antiparallel sequence for a rna/dna polymer
  
  @param polymer
  PolymerNotation
  @return antiparallel sequence
  @throws HELM2HandledException
  if th polymer contains HELM2 features
  @throws RNAUtilsException
  if the polymer is not RNA or DNA
  @throws ChemistryException
  if the Chemistry Engine can not be initialized