Add airframe-http-client implementation for Scala.js:

def get[X](path:String): Future[X] = macro ...

This macro will generate code like this:

        AjaxUtil.call("/v1/query") { response =>
          val codec   = MessageCodec.of[Seq[PrestoQuery]]
          val data = codec.fromMsgPack(response)
          Future(data)
      }

To do so:

• We need to extract common interfaces in airframe-http for Scala and Scala.js.
  • Some package relocation will be necessary (e.g., HttpClient might need to move to wvlet.airframe.http.client)
• Use cross Scala build for airframe-http