Added Prefix params Support + Test (#94)

Thank you!

src/Ben.Demystifier/EnhancedStackTrace.Frames.cs

@@ -511,6 +511,11 @@ namespace System.Diagnostics
 
         private static string GetPrefix(ParameterInfo parameter)
         {
+            if (Attribute.IsDefined(parameter, typeof(ParamArrayAttribute), false))
+            {
+                return "params";
+            }
+
             if (parameter.IsOut)
             {
                 return "out";

test/Ben.Demystifier.Test/ParameterParamTests.cs

@@ -0,0 +1,40 @@
+namespace Ben.Demystifier.Test
+{
+    using System;
+    using System.Diagnostics;
+    using Xunit;
+
+    public class ParameterParamTests
+    {
+        [Fact]
+        public void DemistifiesMethodWithParams()
+        {
+            Exception dex = null;
+            try
+            {
+                MethodWithParams(1, 2, 3);
+            }
+            catch (Exception e)
+            {
+                dex = e.Demystify();
+            }
+
+            // Assert
+            var stackTrace = dex.ToString();
+            stackTrace = LineEndingsHelper.RemoveLineEndings(stackTrace);
+            var trace = string.Join(string.Empty, stackTrace.Split(new[] { Environment.NewLine }, StringSplitOptions.RemoveEmptyEntries));
+
+            var expected = string.Join(string.Empty, new[] {
+                "System.ArgumentException: Value does not fall within the expected range.",
+                "   at bool Ben.Demystifier.Test.ParameterParamTests.MethodWithParams(params int[] numbers)",
+                "   at void Ben.Demystifier.Test.ParameterParamTests.DemistifiesMethodWithParams()"});
+
+            Assert.Equal(expected, trace);
+        }
+
+        private bool MethodWithParams(params int[] numbers)
+        {
+            throw new ArgumentException();
+        }
+    }
+}