LabelledGeneric instances for Sealed Classes

[xuwei-k]

shapeless default implementation can derive scala sealed trait/class

scala> sealed trait XX; case class YY(i: Int) extends XX; case class ZZ(s: String) extends XX
trait XX
class YY
class ZZ

scala> LabelledGeneric[XX]
val res1: shapeless.LabelledGeneric[XX]{type Repr = YY with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("YY")],YY] :+: ZZ with shapeless.labelled.KeyTag[Symbol with shapeless.tag.Tagged[String("ZZ")],ZZ] :+: shapeless.CNil} = shapeless.LabelledGeneric$$anon$2@4b5e8f34