first cut at adding selfplay option
increase center pawn block score
fix variable init order for Search class
include self-play code only if -DSELFPLAY
Merge branch 'selfplay'
Add experimental self-play feature for testing (commented
out in the code by default). If enabled, adds a selfplay
command that will run a match and then exit. One side of the
match has options.search.mod=0 and one side has it set to 1.
This can be used to test code changes. Parameters passed to
selfplay are a PGN opening book file and # of games.