Chapter 5: Exercise 2: Book Library minor updates/clarifications.

Also changes LibraryView to use listenTo instead of on and to use Collection.each instead of _.each.
Merge remote-tracking branch 'upstream/gh-pages' into gh-pages

Conflicts:
	chapters/05-exercise-2.md
Merge pull request #366 from dcmaf/gh-pages

Chapter 5: "Exercise 2 - Book Library" rewording and clarifications