03: Add implemented package
04: Add package & empty files
04: Add option.map
04: Add Option.flatMap
04: Add Option.getOrElse
04: Add Option.orElse
04: Add Option.filter
04: Make None an object (not class); use if guard in Option.filter
04: Implement map and filter using flatMap
04: Add comments
04: Ex. 2, map2 function
04: Ex. 4, sequence function
04: Add comments on excpected test results
04: Ex. 3, better solution from book, plus comment
Merge branch 'master' of https://github.com/mtshared/fpinscala