Fix /redirect to return absolute URL

This should fix #144 

I also added simple tests to `redirect`,`relative-redirect` and `absolute-redirect`
I would write this a little differently personally (but you may disagree with me):

```python
absolute = requests.args.get('absolute', 'False').lower() == 'true'
```

If someone does `GET /redirect/10?absolute=True` then I would expect us to handle it similarly to the having a lowercase `T` in `True`. Make sense?