code: public <R> R forEach(def<R> func) {
                  return forThose((k, v) -> true, func);
          }
docs: define a function to deal with each entry in the map
  
  @param func a function returns 'last loop result'
  @return return 'last loop value'.<br>
  check
  <a href="https://github.com/wkgcass/Style/">tutorial</a> for
  more info about 'last loop value'