code: public void observeVariables(List<String> variableNames, VariableObserver observer)
  			throws StoryException, Exception {
  		for (String varName : variableNames) {
  			observeVariable(varName, observer);
  		}
  	}
docs: Convenience function to allow multiple variables to be observed with the same
  observer delegate function. See the singular ObserveVariable for details. The
  observer will get one call for every variable that has changed.
  
  @param variableNames
  The set of variables to observe.
  @param observer
  The delegate function to call when any of the named variables
  change.
  @throws Exception
  @throws StoryException