Added test for Traversable.collect
Added test for Traversable.count.
Added test for Seq.diff.
Added test for Traversable.drop
Added test for Traversable.dropWhile.
Added test for Traversable.exists.
Added test for Traversable.filter.
Added test for Traversable.filterNot.
Added test for Traversable.find.
Added test for Traversable.flatten.
Added test for Traversable.flatMap.
"TODO" replaced with editor-fold.