* opt: only skip one value when call Iterator.HasNext()
* feat: V_NONE supports Set() and Add()
* feat: add node type V_ANY
* feat: ast.Node implements `json.Unmarshaler`
* fmt: use space instead of tab for indent
* feat: node V_ANY cast to Bool()\Int64()\Float64()\String()\Number()\Map()\Array()Interface()
* feat: V_NULL supports Set() and Add()
Co-authored-by: duanyi.aster <duanyi.aster@bytedance.com>