Ability to ignore unused parameters instead of failing the command. (#915)

* Addition of FailOnTooManyArgs

* Correct name & only pass in bool

src/Discord.Net.Commands/CommandServiceConfig.cs

@@ -15,5 +15,8 @@
 
         /// <summary> Determines whether RunMode.Sync commands should push exceptions up to the caller. </summary>
         public bool ThrowOnError { get; set; } = true;
+
+        /// <summary> Determines whether extra parameters should be ignored. </summary>
+        public bool IgnoreExtraArgs { get; set; } = false;
     }
 }