2.5.20 released October 10, 1999

- tuning
- 13 helpers replaced by constraints
- action lines introduced in the patterns database to complement the
  constraints
- zero-valued joseki moves now generate antisuji moves (only effective in
  the new move generation scheme)
- more experimental move generation code
- new file: src/move_reasons.c
- bugfix in load_sgf_file()
- many new eye patterns
- cleanup in liberty.h and optics.c
- new diagnostics in compute_eyes()
- in basicnet4 we only consider safe attacking moves
- speedup in basicnet4 for isolated stones and probably other strings