Rename chapter -> section

data/section2/apartment_train.csv

data/section2/apartment_val.csv

data/section2/bat_test_data.csv

data/section2/bat_train_data.csv

data/section4/class_test_data.npy

data/section4/class_train_data.npy

data/section4/model_0

data/section4/model_1

data/section4/model_2

data/section5/concrete_data.csv

data/section6/MNIST_test_data.npy

data/section6/MNIST_train_data_labeled.npy

data/section6/MNIST_train_data_unlabeled.npy

data/section7/winequality-red.csv

data/section7/winequality-white.csv

section2.py

section3.py

section4.py

section5.py

section6.py