Clone instead of move _url fields with the simple link parser

Fixes issues with data like this:

```
{
  "config": {
    "some_configured_url": "http://example.com"
  }
}
```

Currently, this 'real' url is buried behind `resource.config.rels[:some_configured].href`. Now they're copied, so it'll still be available at `resourece.config.some_configured_url`.

Fixes issues with octokit when fetching webhooks (the example above) and statuses (which have a `target_url`).