Only render fg cells if there are changes

src/Types.ts

@@ -16,5 +16,6 @@ export type LinkMatcherValidationCallback = (uri: string, element: HTMLElement,
 export type CustomKeyEventHandler = (event: KeyboardEvent) => boolean;
 export type Charset = {[key: string]: string};
 
+// TODO: Add code here?
 export type CharData = [number, string, number];
 export type LineData = CharData[];