DOC: Edits for book 2 chapter 2.

DOC: Added SecondDerivativeRecursiveGaussianImageFilter example.

Change-Id: Ife86e17cd85ae5b8366d7ea71622d4fe5186674e
Merge topic 'book-2-chapter-2-edits'

62ea1a48 DOC: Edits for book 2 chapter 2.