Chap 8: Ex6: uniform and Double choose.
Chap 8: Generating pairs
Chap 8: Introducing Gen case clas
Desugaring cross's for comprehension.Just for kicks
Revert "Desugaring cross's for comprehension.Just for kicks"

This reverts commit f30ec6a78a1fcc66cf56ba6851475ebb6e9c24d1.
Chap 8: cross now correctly identifies unbondedness
Chap 8: Generalize pairOf
Chap 8: adding .map and .flatMap to enrich Gen.
Chap 8: Ex7: Using map for choose(Double,Double)
Chap 8: Ex7: map2 (used in pair)
Chap 8. Ex8. (sameParity needed only map. it's probably wrong)