Decode server_name, script_name, path_info as UTF-8

This is a first attempt at fixing #61 .  Unfortunately I don’t really understand how Klein works thus I’m not sure how to handle errors here, I’ve marked the relevant positions with XXX.  

Any advice from @dreid would be super-awesome.

***

I also have to admit that I don’t understand how/why the

```python
        kleinRequest = IKleinRequest(request)
        kleinRequest.mapper = mapper
```

block works but that’s a story for another day. :)