Add in the prettyprinting bit in the svd example, which still doesn't work yet properly in master.

examples/src/svd.rs

@@ -180,5 +180,10 @@ fn main() {
                         devattributes: dev_attrs
                     };
     
-    println!("{:?}", yaserde::ser::to_string(&dev).ok().unwrap());
+    // Display pretty printed XML
+    let yaserde_cfg = yaserde::ser::Config{
+        perform_indent: true,
+        .. Default::default()
+    };
+    println!("{:#?}", yaserde::ser::to_string_with_config(&dev, &yaserde_cfg));
 }