add Cell::is_null()
add previous_free_pair_index;
add previous_free_cell_index;

to release used cell, pair memory.
use previous_free_pair_index, previous_free_cell_index to
  release used cell, pair memory.
move CString in to class. move std namespace position
move std namespace position
add non_os_repl()
refine history function, don't clear all line to blank
refine head files
change history order
add
  do_eval()
  int tokenize(const char *s, TokenContainer &tokens, int
    &parenthesis_count)

  call do_eval() do eval.
add non_os_repl()
deque, line_buf change global variable to local variable
Merge branch 'mm'
fixed for OS_CPP macro compie right.

do_eval(): release cell, pair pool free index.

Deque<DS::CString> deque; => DS::Deque<DS::CString> deque;

move
  previous_free_pair_index = free_pair_index;
  previous_free_cell_index = free_cell_index;
to near read().