Remove trailing whitespace
HList split methods reverted to return Tuple2 (to maintain back compatibility)

Coproduct.split methods changed to return Either
Added HList.splitP & Coproduct.splitC methods that return products / coproducts.
Merge pull request #223 from stacycurl/revert-split

HList split methods reverted to return Tuple2
Added HList.{partition, partitionP} & Coproduct.{partition, partitionC}

Reimplemented Filter & FilterNot type classes in terms of Partition
  (for both HList & Coproduct)