added more verbose stringify for object

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #46
| License       | BSD

This PR makes the result of `StringUtil::stringify()` more verbose, so that finding out why the match failed is allot easier.

I'm not sure if setting the objects graph to be exported should be enabled by default.