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