Use a const for all refs to data char and width

Part of #791

src/Renderer.ts

@@ -4,6 +4,7 @@
 
 import { ITerminal } from './Interfaces';
 import { DomElementObjectPool } from './utils/DomElementObjectPool';
+import { CHAR_DATA_WIDTH_INDEX, CHAR_DATA_CHAR_INDEX } from './Buffer';
 
 /**
  * The maximum number of refresh frames to skip when the write buffer is non-
@@ -168,8 +169,8 @@ export class Renderer {
       for (let i = 0; i < width; i++) {
         // TODO: Could data be a more specific type?
         let data: any = line[i][0];
-        const ch = line[i][1];
-        const ch_width: any = line[i][2];
+        const ch = line[i][CHAR_DATA_CHAR_INDEX];
+        const ch_width: any = line[i][CHAR_DATA_WIDTH_INDEX];
         const isCursor: boolean = i === x;
         if (!ch_width) {
           continue;