[chapter 06 #131] Substitute Algorithm: add readme
[chapter 06 #131] Substitute Algorithm: add example
[chapter 06 #132] Substitute Algorithm: refactored example
[chapter 06 #133] Replace Loop with Collection Closure Method: add readme
[chapter 06 #135] Extract Surrounding Method: add readme
[chapter 06 #139] Introduce Class Annotation: add readme
[chapter 06 #141] Introduce Class Annotation: add example
[chapter 06 #141] Introduce Class Annotation: Convert the original method to a class method
[chapter 06 #141] Introduce Class Annotation: delete original method by calling class method
[chapter 06 #141] Introduce Class Annotation: refactored example