Added row() function.

lib/src/sunmi_col.dart

@@ -0,0 +1,34 @@
+/*
+ * flutter_sunmi_printer
+ * Created by Andrey U.
+ * 
+ * Copyright (c) 2020. All rights reserved.
+ * See LICENSE for distribution and usage details.
+ */
+
+import 'enums.dart';
+
+/// Column contains text, align and width (an integer in 1..12 range)
+class SunmiCol {
+  SunmiCol({
+    this.text = '',
+    this.width = 2,
+    this.align = SunmiAlign.left,
+  }) {
+    if (width < 1 || width > 12) {
+      throw Exception('Column width must be between 1..12');
+    }
+  }
+
+  String text;
+  int width;
+  SunmiAlign align;
+
+  Map<String, String> toJson() {
+    return {
+      "text": text,
+      "width": width.toString(),
+      "align": align.value.toString(),
+    };
+  }
+}