code: public AppHelper add(String name, String displayValue, String description, String defaultValue)
      {
          Arguments.add(new Argument(name, displayValue, description, defaultValue));
          return this;
      }
docs: Adds an argument to this application helper.
  
  @param name the (case-sensitive) argument name.
  @param displayValue the display value to be shown in the usage print-out for this argument.  For instance, a number or specific expected format.
  @param description the description for the argument to be displayed in the usage print-out.
  @param defaultValue the default value (as a String) to be used for an optional argument.  If no default value is provided, the argument will be required in the command line call.
  @return reference to this application helper, allowing command-chaining.