Added ServiceNotFoundException

- When Ask/RPC calling the exception will now be ServiceNotFoundException instead of Exception

src/Holon/Namespace.cs

@@ -152,7 +152,7 @@ public async Task SetupAsync() {
                         _replyWaits.Remove(e.ID);
                     }
 
-                    tcs.TrySetException(new Exception("The envelope was returned before delivery"));
+                    tcs.TrySetException(new ServiceNotFoundException("The envelope was returned before delivery"));
                 }
             };
 

src/Holon/Services/ServiceNotFoundException.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Holon.Services
+{
+    /// <summary>
+    /// Represents an exception which occurs when a service cannot be found.
+    /// </summary>
+    public class ServiceNotFoundException : Exception
+    {
+        /// <summary>
+        /// Creates a new service not found exception.
+        /// </summary>
+        public ServiceNotFoundException() {
+        }
+
+        /// <summary>
+        /// Creates a new service not found exception.
+        /// </summary>
+        /// <param name="message">The message.</param>
+        public ServiceNotFoundException(string message) : base(message) {
+        }
+
+        /// <summary>
+        /// Creates a new service not found exception.
+        /// </summary>
+        /// <param name="message">The message.</param>
+        /// <param name="innerException">The inner exception.</param>
+        public ServiceNotFoundException(string message, Exception innerException) : base(message, innerException) {
+        }
+    }
+}