Add .idea the intellij project directory to .gitignore.
Merge pull request #314 from HappyRay/master

Add .idea the intellij project directory to .gitignore.
Add answer/hint for Chapter 2, Exercise 3
Remove and reorder excercises to match final version of the book.
Merge pull request #318 from Jazzatola/answerfix

Add answer/hint for Chapter 2, Exercise 3
Remove editorial comment
Update 03.answer.scala

Should be `&&` instead of `||`
Update and rename 19.answer.scala to 19.answer.markdown
Update 19.answer.markdown
Update 19.answer.markdown
Update 19.answer.markdown
Update README.md
Implement unfold via Option fns. Closes #325.
Merge pull request #330 from balajisivaraman/stream-unfold

Implement unfold via Option fns. Closes #325.
fix compilation error for 05.answer.scala in chapter 12
Update 05.answer.scala
Update 04.hint.txt
Update 05.hint.txt
Update 07.hint.txt
Update 13.hint.txt