https://docs.unity3d.com/Packages/com.unity.nuget.newtonsoft-json@3.2/manual/index.html 유니티에서 공식으로 제공하는 Newtonsoft Json Unity Package 사용하기
based on JSON.NET For Unity
modify namespace. use Fiveminlab.Newtonsoft.Json instead of Newtonsoft.Json.
copy <unity_engine>/Editor/Data/Managed/UnityEngine.dll to 3rdParty/