Fixed a bug that caused AST to be processed as a string when constructing an AST from a Json null.#74

## Fixed bug where Json Arrays are nested together if they are joined together. ``` JsonArray(["A", "B"]) ++ JsonArray(["C", "D"]) ~1.3.3 JsonArray(["A", "B", ["C", "D"]]) 1.3.4 ~ JsonArray(["A", "B", "C", "D"]) ``` However, if the AST to be joined is not a JsArray, it will be nested. ## Fix bug where building an AST from json null and reserializing it would result in a "null" literal ```json {"value": null} ``` Deserialize for ```scala case class Nullable(value: Object) ``` Serialize for ```json {"value": "null"} ``` ## Some codec definition syntax has been added. ### Determine the deserialize result and convert it to a different type. Improve problem where some function names were too abstract to be used because they could not be overloaded with other definitions (Tom) Added syntax list ```scala ReadWith[String]("status") .readMap { case "success" => ReadWith[String]("body") case "failure" => ReadWith[String]("error") } .deserialize( Json.obj( "status" -> "success", "body" -> "test1", "error" -> "test2" ) ) ``` There is no control over serialization. the Serialize function will do what you need. ## Add a pure key to the codec. ```scala ReadWith[String]("aa").deserialize( Json.obj( "aa" -> "bb" ) ) == "bb" ``` This is a syntax sugar for the Serialize / Deserialize / Format function. `ReadWith[T: Read]`, `WriteWith[T: Write]`, `BothWith[T: Codec]`