Evidence indicator feed about libspn

[anicolson]

So i just use indicator_y_data = [[-1], [-1], [-1], [-1]] instead of indicator_y_data = [[0], [0], [0], [0]], and it works (output of 1.0 for no evidence). So I asume indicator_y_data = [[-1], [0], [1], [2]] would give outputs for the root, the first weight of the root, the second weight of the root, and then the third weight of the root.