A third CLI argument is now accepted, describing a score goal.
The program will then treat reaching this score as a win and
calculate lines optimized for this score, ignoring any (possible)
higher scores.
Outputting of probabilities is now done in unified way.
This ensures that we can handle both rational and floating-point
probabilities in all program parts properly.
The compile-time macro
NUSE_RATIONAL_PROBABILITIES
can now be defined to use floating-point probabilities instead
of real rational ones.
Using floating-point results in roughly 10% speedup.
