optimized NonEmptyList foldRight1. avoid stackoverflow
add NonEmptyList test
add test "foldRight1 is reduceRight"
relaxed constraints HeapFunctions.sort and HeapFunctions.sortWith
Merge pull request #425 from xuwei-k/request/non-empty-list-foldright1

optimized NonEmptyList foldRight1. avoid stack overflow
Merge pull request #426 from xuwei-k/request/heap-functions

relaxed constraints HeapFunctions.sort and HeapFunctions.sortWith