fixed factor signature for applicative exercises
Omit an optional type variable of the Stream.filter method.

The type variable [B] of the fpinscala.lazyness.Stream.filter method
can be omitted.
08.answer.scala was the same as 07.answer.scala for chapter 9
fix for Traverse.mapAccum
Issue #334
Simplify answer to exercise 5.2
Prevent unnecessary evaluations

Previous implementation of drop did not handle 
    
    Stream.cons(0, ???).take(1)
Proper comments on take(n) and drop(n)
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
Merge pull request #341 from psliwa/patch-1

fix compilation error for 05.answer.scala in chapter 12
fpinscala-parallelism: Explains that the example map2 is semantically incorrect
Add traverse and sequence signature.
Merge pull request #344 from ralphcollett/master

Add traverse and sequence signature.
Update 01.answer.scala
Merge pull request #343 from mosesn/par-correct

fpinscala-parallelism: Explains that the example map2 is semantically incorrect