added output format arg

src/CodeCoverageSummary/CommandLineOptions.cs

@@ -6,5 +6,8 @@ namespace CodeCoverageSummary
     {
         [Value(index: 0, Required = true, HelpText = "Code coverage file to analyse.")]
         public string Filename { get; set; }
+
+        [Option(shortName: 'f', longName: "format", Required = false, HelpText = "Output Format.", Default = "text")]
+        public string Format { get; set; }
     }
 }