improve getRandomPiece
debug getRandomPiece
modify the implement of SetNode and getSet, greatly improve the efficiency, delete the old codes
1. use game_ending as the random threshold (faster)

2. give up the discrete set, delete the stack
change ignore, enlarge the set_static_size
Rend
Complete with 200 games
Miss something
70 games (to save time)
use the same board to test, add function time statistics.