anchor.diff:  Not implemented in java port, yet.
   Not implemented in bash port, yet, but doable by reading from internal variables. (They may change unexpectedly!)
   
  -===== Customizing the automatic help message
  +==== Customizing the automatic help message
   
   ----
   void CheckArg::set_posarg_help(const std::string &usage, const std::string &descr );
  
positive.code: 
  
  [[long-only-val]]
  ===== Long only with value
  
  ----
  int CheckArg::add(const std::string &lopt, const std::string &help, bool has_val=false);            // <1>
  
negative.code: Number of positinal arguments in array returned by `checkarg_pos_args`.
  
  [[show_help]]
  ==== Show help messages
  
  ----
  void CheckArg::show_help()
  