Drafts for exercises in chapter 3 and 4
Draft of chapter 4
Sketch of Chapter 5
chap05 draft
Exercise 6 alpha version
RC for chap05
Exercise 6 Haskell files
Merge branch 'master' into victor-draft
Chapter 4 compiles
Chapter 4

Signed-off-by: Víctor López Juan <victor@lopezjuan.com>
Chapter 3