Simplify Bullfight (C#) folder structure

17_Bullfight/csharp/RiskLevel.cs

@@ -0,0 +1,12 @@
+namespace Game
+{
+    /// <summary>
+    /// Enumerates the different levels of risk for manoeuvres in the game.
+    /// </summary>
+    public enum RiskLevel
+    {
+        Low,
+        Medium,
+        High
+    }
+}