Added CommandService logging

src/Discord.Net.Commands/CommandException.cs

@@ -0,0 +1,15 @@
+using System;
+
+namespace Discord.Commands
+{
+    public class CommandException : Exception
+    {
+        public CommandInfo Command { get; }
+        public ICommandContext Content { get; }
+
+        public CommandException(CommandInfo command, ICommandContext context, Exception ex)
+            : base($"Error occurred executing {command.GetLogText(context)}.", ex)
+        {
+        }
+    }
+}