added marr.datamapper source code for easy debugging.

Marr.Data/DataMappingException.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+
+namespace Marr.Data
+{
+    public class DataMappingException : Exception
+    {
+        public DataMappingException()
+            : base()
+        {
+        }
+
+        public DataMappingException(string message)
+            : base(message)
+        {
+        }
+
+        public DataMappingException(string message, Exception innerException)
+            : base(message, innerException)
+        {
+        }
+    }
+}