Use better exception to represent unsupported converter

ArcToolkitCLI/Commands/Converters/BaseConverter.cs

@@ -19,7 +19,7 @@ namespace ArcToolkitCLI.Commands.Converters
             var verb = GetType().GetCustomAttributes(typeof(VerbAttribute), true).Cast<VerbAttribute>().FirstOrDefault();
             
             if(verb == null)
-                throw new NotImplementedException("The converter is not properly implemented yet, sorry!");
+                throw new NotSupportedException("The converter is not properly implemented yet, sorry!");
 
             var convertCommand = verb.Name;