CUETools.Flake: better use of new window functions

CUETools.Codecs.FLAKE/StereoMethod.cs

@@ -3,11 +3,13 @@ namespace CUETools.Codecs.FLAKE
 {
 	public enum StereoMethod
 	{
-		Independent = 0,
-		Estimate = 1,
-		Evaluate = 2,
-        Search = 3,
-        EstimateX = 4,
-        EvaluateX = 5,
+        Invalid,
+		Independent,
+		Estimate,
+		Evaluate,
+        Search,
+        EstimateX,
+        EvaluateX,
+        EstimateFixed,
     }
 }