Converts parameter array back into matrices.

def __roll(self, unrolled):
        """Converts parameter array back into matrices."""
        rolled = []
        index = 0
        for count in range(len(self.__sizes) - 1):
            in_size = self.__sizes[count]
            out_size = self.__sizes[count+1]
            theta_unrolled = np.matrix(unrolled[index:index+(in_size+1)*out_size])
            theta_rolled = theta_unrolled.reshape((out_size, in_size+1))
            rolled.append(theta_rolled)
            index += (in_size + 1) * out_size
        return rolled