Make Tuple code follow typeclass pattern
Add some comments
Merge pull request #430 from twitter/feature/tuple-typeclasses

Make Tuple code follow typeclass pattern
convert Monoid to Semigroup
Merge pull request #431 from twitter/semigroupthethings

convert Monoid to Semigroup
Relax Iterable to TraversableOnce
Fixup Mappable
Make sum the same as plus in the Fields API
fix a few tests
Fix Tutorial
fix comment
Merge pull request #433 from twitter/fixsum

Merge #433
Merge pull request #432 from twitter/travonce

Merge #432