code: public <R> R forEach(RFunc1<R, T> func, int index) {
                  return forEach($(func), index);
          }
docs: define a function to deal with each element in the list with given
  start index
  
  @param func
  a function takes in each element from list and returns
  last loop value
  @param index
  the index where to start iteration
  @return return 'last loop value'.<br>
  check
  <a href="https://github.com/wkgcass/Style/">tutorial</a> for
  more info about 'last loop value'