add `modVars` to `SugarCubeStoryVariables`

sugarcube/src/interfaces.d.ts

@@ -178,6 +178,7 @@ declare module "twine-sugarcube" {
 		location_var: object;
 		locationTravelRequest?:LocationTravelRequest;
 		media_path: string;
+		modVars:any;
 		quest: (id:string)=>Quest;
 		result: number | string;
 		/**

sugarcube/src/version/VersionControl.ts

@@ -15,6 +15,8 @@ class VersionControl{
 			variables.q._quests['mother_virgin'].certificateDeadline = new Date(0);
 		}
 		
+		variables.modVars ??= {};
+
 		variables.version = toVersion;
 		
 	}