If macros example

ifmacros.scala

```scala
implicit def decoder
    #IF-SCALA < 2.13
        [C[A] <: Traversable[A]](implicit cbf: MyCollection.CBF1[C],cbf2: MyCollection.CBF2[C]): Decoder[MyCollection[C]]
    #ELSE
        [C[A] <: Traversable[A]](implicit builder: Builder[C]): Decoder[MyCollection[C]]
    #DONE    
= new Decoder[MyCollection[C]] {
      override def apply(c: HCursor): Decoder.Result[MyCollection[C]] = {
        (
          c.downField("stuff").as[Option[C[Wrapper]]] |@|
          c.downField("recursive_stuff").as[Option[C[MyCollection[C]]]]
        ).map(MyCollection.apply)
      }
    }
    
def getMyCollection2
    #IF-SCALA < 2.13
        [C[A] <: Traversable[A]](implicit cbf: MyCollection.CBF1[C],
                                 cbf2: MyCollection.CBF2[C]): MyCollection[C]
    #ELSE
        [C[A] <: Traversable[A]](implicit builder: Builder[C]): MyCollection[C]
    #DONE    
= {
    val jsonString = """
      {
          "stuff": ["a", "b"],
          "recursive_stuff": [{
              "stuff": ["c"]
          }]
      }
    """
    val json = io.circe.parser.parse(jsonString).right.get
    json.as[MyCollection[C]].right.get
}
```