Path for nested `urls.py` files not properly built.

I have a project level `nestor/urls.py` file like this:

```python
urlpatterns = [
url(r'^v1/', include('nestor.v1.urls', namespace='api-v1')),
url(r'^docs/', include('rest_framework_docs.urls', namespace='api-docs')),
]
```

Then `nestor/v1/urls.py` like:
```python
router = rest_framework.routers.DefaultRouter()

router.register('node', Node, base_name='node')
router.register('vm', VirtualMachine, base_name='vm')
router.register('ldev', LDev, base_name='ldev')

# BUG: DRFDocs is not picking up the nesting properly
urlpatterns = [
url(r'^', include(router.urls)),
]
```

The generated URLs in the doc look like:

```
/node/
/node//
/vm/
/vm//
/vm//reboot/
/ldev/
/
```

Clearly, the `v1/` prefix is missing. I think the culprit is the recursive part of the endpoint generator:

https://github.com/manosim/django-rest-framework-docs/blob/master/rest_framework_docs/api_docs.py#L27

In that line, the `parent_patter` that was carried in the recursive call is replaced and not accumulated.

Also, I have the impression that @manosim has stopped working on the package.

Inspect rest_framework_docs/api_docs.py around line 27, focusing on how the recursive endpoint generator carries the parent pattern. Verify the generated documentation using the nested nestor/urls.py and nestor/v1/urls.py configuration shown in the issue. Done means endpoints under the v1 include are documented with the v1/ prefix.

Written by the indexing model from the issue text.