add matestats.py script

[robertnurnberg]

Sample usages:

> python matestats.py matetrack.epd --cutOff 50 --debug
Loaded 6554 EPDs with abs(bm) in [1, 126].
Average length of bm mates in plies is 20.15.
ply frequencies: 1: 4, 3: 17, 5: 23, 7: 67, 9: 186, 10: 1, 11: 378, 12: 4, 13: 1700, 14: 3, 15: 1020, 16: 5, 17: 671, 18: 3, 19: 585, 20: 3, 21: 401, 22: 1, 23: 331, 25: 209, 26: 1, 27: 148, 28: 1, 29: 129, 31: 100, 32: 1, 33: 75, 35: 60, 36: 1, 37: 41, 39: 45, 41: 40, 43: 26, 45: 19, 47: 23, 49: 9, 51: 16, 53: 9, 55: 8, 57: 7, 59: 23, 61: 10, 63: 10, 65: 3, 67: 6, 69: 8, 71: 5, 73: 2, 75: 4, 77: 4, 79: 4, 81: 4, 83: 4, 85: 8, 87: 3, 89: 4, 91: 3, 92: 1, 93: 4, 95: 2, 97: 2, 99: 10, 101: 2, 105: 1, 107: 1, 109: 2, 111: 2, 113: 4, 115: 1, 117: 1, 119: 4, 121: 1, 123: 2, 125: 1, 127: 4, 129: 1, 131: 2, 133: 1, 134: 1, 137: 3, 139: 1, 141: 1, 143: 3, 147: 1, 149: 1, 153: 1, 163: 1, 173: 1, 177: 1, 185: 2, 191: 1, 199: 1, 201: 1, 203: 1, 205: 1, 217: 1, 219: 1, 237: 1, 239: 1, 241: 2, 251: 1
Saved bm distribution plot in file matetrack.png.

> python matestats.py mates2000.epd --debug
Loaded 2000 EPDs with abs(bm) in [1, 27].
Average length of bm mates in plies is 15.45.
ply frequencies: 1: 1, 2: 5, 3: 7, 4: 5, 5: 5, 6: 27, 7: 22, 8: 47, 9: 34, 10: 92, 11: 62, 12: 351, 13: 281, 14: 203, 15: 136, 16: 112, 17: 100, 18: 87, 19: 66, 20: 47, 21: 47, 22: 35, 23: 38, 24: 27, 25: 26, 26: 15, 27: 19, 28: 22, 29: 16, 30: 9, 31: 8, 32: 3, 33: 10, 34: 4, 35: 4, 36: 4, 37: 4, 38: 1, 39: 3, 40: 6, 41: 3, 42: 1, 43: 1, 44: 1, 47: 1, 49: 1, 54: 1
Saved bm distribution plot in file mates2000.png.