Version 3.0 to 3.1b1

- Fixed some minor bugs (e.g. added BUG(argc < 1) in main).
- Updated comments.
- Added score_t (score was always long).
- Added PVM support (Parallel Virtual Machine).
- Changed pv_ to root_ because the names resembled the PVM names.
- Added handle_signal to allow for interrupts (not used yet).
- Added store_game. Needed for PVM to broadcast the moves.

Version 3.1b1 to 3.1b2
- Added draughts program.

Version 3.1b2 to 3.2b1
- All moves are generated in alpha_beta so that an index to the best move
  can be stored in the hash table, not the move itself (simpler).
- The pawn structure is not updated any more in do_move, but calculated in
  set_attack_board (simpler).
- The castling bonus is not given any more in do_move, but calculated in 
  return_pos_score (better).
- Threat extensions are no longer dependent on beta (better).
- Added MSDOS support. Required change of some data structures to reduce 
  memory usage.
- Added gen_code to draughts program.

Version 3.2b1 to 3.2b2
- Added display_var (no best variation if small hash table).

Version 3.2b2 to 3.3b1
- Added Standard Algebraic Notation.
- Added a simple PGN reader.
- do_move now handles swapping of my_colour and your_colour (simpler)
- Added mate finder.

Version 3.3b1 to 3.3b2
- The stacks for the move generation are better handled in pgn, so that
  large databases can be searched.
- anal_pgn now prints a summary when searching for transpositions.

Version 3.3b1 to 3.31
- Added a draughts endgame database generator.

Version 3.31 to 3.31p1
- Fixed some bugs in the draughts endgame database generator.

Version 3.31 to 3.4
- FEN positions descriptions are now used throughout.
- The threat extensions have been removed (the code got too messy with the
  PVM code). They will be reintroduced in 3.5.
- The parallel code has been rewritten from scratch. The program should now also
  run on massively parallel machines.
- The opening book code has been rewritten from scratch. A btree-indexed database
  with FEN positions is now used.
- The PGN database reader now also checks for duplicate games by storing 32
  bit CRC's in a btree. It can also tag games with an opening code.
- Some settings can also be read from a configuration file .zzzzzzrc.
- A perl script for letting zzzzzz play on the Internet Chess Server is included.
