def split_list(lis, fraction):
		if fraction != 1.0:
			l = len(lis)
			cutoff = int(math.ceil(l * fraction))
			return lis[0:cutoff], lis[cutoff:]
		else:
			return lis, []
split a list into 2 lists based on the fraction provided. Used to break the instances into 
dataset/ETHPy150Open japerk/nltk-trainer/train_classifier.py/split_list