Enable ^FV command (needed for UPS) (#195)

* Enable ^FV command

- Based off ^FD

src/BinaryKits.Zpl.Viewer/CommandAnalyzers/FieldDataZplCommandAnalyzer.cs

@@ -16,7 +16,7 @@ public class FieldDataZplCommandAnalyzer : ZplCommandAnalyzerBase
         private static readonly Regex qrCodeFieldDataMixedRegex = new Regex(@"^D\d{4}[0-9A-F-a-f]{2},(?<correction>[HQML])(?<input>[AM]),(?<data>.+)$", RegexOptions.Compiled);
         private static readonly Regex qrCodeFieldDataModeRegex = new Regex(@"^(?:[ANK]|(?:B(?<count>\d{4})))(?<data>.+)$", RegexOptions.Compiled);
 
-        public FieldDataZplCommandAnalyzer(VirtualPrinter virtualPrinter) : base("^FD", virtualPrinter) { }
+        public FieldDataZplCommandAnalyzer(VirtualPrinter virtualPrinter, string prefix="^FD") : base(prefix, virtualPrinter) { }
 
         ///<inheritdoc/>
         public override ZplElementBase Analyze(string zplCommand)

src/BinaryKits.Zpl.Viewer/CommandAnalyzers/FieldVarialbleZplCommandAnalyzer.cs

@@ -0,0 +1,14 @@
+namespace BinaryKits.Zpl.Viewer.CommandAnalyzers
+{
+    // todo: fix virtual printer, must enable the MC command
+    // todo: factor out common parts from FieldDataZplCommandAnalyzer so both can inherit
+    // This is currently just a hack to be able to visualize single ups zpl.
+    // The FV command is normally used with the MC command when printing multiple labels of a same pattern.
+    // The MC command allows us to "save" the first label as a template
+    // using FDs as static elements of template and FVs as variable parts.
+    // Subsequent labels only require FV to draw the variable parts.
+    public class FieldVariableZplCommandAnalyzer : FieldDataZplCommandAnalyzer
+    {
+        public FieldVariableZplCommandAnalyzer(VirtualPrinter virtualPrinter): base(virtualPrinter, "^FV") { }
+    }
+}

src/BinaryKits.Zpl.Viewer/ZplAnalyzer.cs

@@ -48,6 +48,7 @@ public AnalyzeInfo Analyze(string zplData)
                 new FieldBlockZplCommandAnalyzer(this._virtualPrinter),
                 new FieldHexadecimalZplCommandAnalyzer(this._virtualPrinter),
                 new FieldNumberCommandAnalyzer(this._virtualPrinter),
+                new FieldVariableZplCommandAnalyzer(this._virtualPrinter),
                 new FieldReversePrintZplCommandAnalyzer(this._virtualPrinter),
                 new LabelReversePrintZplCommandAnalyzer(this._virtualPrinter),
                 new FieldSeparatorZplCommandAnalyzer(this._virtualPrinter, fieldDataAnalyzer),