added Error.Message method

error.go

@@ -66,6 +66,10 @@ func (e *Error) Error() string {
 	return b.String()
 }
 
+func (e *Error) Message() string {
+	return e.msg
+}
+
 // Is implements the error equality function used by errors.Is()
 // It returns true if the error is the same instance or is created using the same ErrTmpl
 func (e *Error) Is(target error) bool {