added GS * command (print image)

lib/src/commands.dart

@@ -46,4 +46,5 @@ const cFeedN = '${esc}d'; // Print and feed n lines [N]
 const cReverseFeedN = '${esc}e'; // Print and reverse feed n lines [N]
 
 // Bit Image
-const cImgPrint = '${gs}v0'; // Print raster bit image [obsolete command]
+const cRasterImg = '${gs}v0'; // Print raster bit image [obsolete command]
+const cBitImg = '$esc*'; // Set bit image mode

lib/src/printer.dart

@@ -329,7 +329,7 @@ class Printer {
     const int densityByte =
         (highDensityVertical ? 0 : 1) + (highDensityHorizontal ? 0 : 2);
 
-    final List<int> header = List.from(cImgPrint.codeUnits);
+    final List<int> header = List.from(cRasterImg.codeUnits);
     header.add(densityByte);
     header.addAll(_intLowHigh(widthBytes, 2));
     header.addAll(_intLowHigh(heightPx, 2));