Add prin for HList, shows how to implement HList funtionalities

hlistprint.scala

                                                                                                               
import shapeless._, record._, ops.record._ , syntax.singleton._, labelled._                                        
                                                                                                                   
object console extends App {                                                                                       
                                                                                                                   
  trait Print[T <: HList] {                                                                                        
    def print(t: T): String                                                                                        
  }                                                                                                                
                                                                                                                   
  object Print {                                                                                                   
    implicit val phnil: Print[HNil] = new Print[HNil] {                                                            
      def print(t: HNil): String = "HNil"                                                                          
    }                                                                                                              
                                                                                                                   
    implicit def pcons[H, T <: HList](implicit pt: Print[T]) = new Print[H :: T] {                                 
      def print(t: H :: T): String =                                                                               
        s"(${t.head.toString} : ${t.head.getClass.getSimpleName}) :: ${pt.print(t.tail)}"                          
    }                                                                                                              
  }                                                                                                                
                                                                                                                   
  implicit class PrintOpsi[T <: HList](t: T) {                                                                     
    def print(implicit p: Print[T]) = p.print(t)                                                                   
  }                                                                                                                
                                                                                                                   
  val l = 1 :: "ciao" :: false :: HNil                                                                             
  println(s"res: ${l.print}")                                                                                      
                                                                                                                   
}