Cleanup in chapter 2's exercises and remarks in chapter 3

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>
Chapter 3: tie it all together

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>
Begin chapter on dual lattice and Fourier analysis

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>
Minor cleanups

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>
Section on lattice width

Signed-off-by: Nicolai Hähnle <haehnle@or.uni-bonn.de>