wip

```
scala> case class Foo(a: Int, b: String)
defined class Foo

scala> import shapeless.contrib.argonaut._
import shapeless.contrib.argonaut._

scala> shapeless.contrib.argonaut.deriveEncodeJson[Foo].encode(Foo(111, "xxxx"))
res0: argonaut.Json = {"b":"xxxx","a":111}
```