Simplify Mastermind (C#) folder structure

60_Mastermind/csharp/Command.cs

@@ -0,0 +1,13 @@
+namespace Game
+{
+    /// <summary>
+    /// Enumerates the different commands that the user can issue during
+    /// the game.
+    /// </summary>
+    public enum Command
+    {
+        MakeGuess,
+        ShowBoard,
+        Quit
+    }
+}