add Foldable#to

like scala.collection.GenTraversableOnce#to
https://github.com/scala/scala/blob/v2.10.2/src/library/scala/collection/GenTraversableOnce.scala#L565-L574
add test for Foldable#to
Merge pull request #420 from xuwei-k/request/foldable-to

add Foldable#to