attach error-information to url on redirect

i had the same problem as @zerrvox at #7

after declining (implicit, for the sake of simplicity) the response looked like the following one:

```
$ curl 'api.hfcit.dev/oauth/authorize?response_type=code&client_id=4a69dd44-fdf4-4c34-8fae-b8ef40818657&redirect_uri=http://foo.bar&state=123' | json
HTTP/1.1 302 Found
Server: nginx/1.7.0
Content-Type: application/json
Transfer-Encoding: chunked
Connection: keep-alive
Cache-Control: no-cache
Date: Sun, 27 Apr 2014 17:47:37 GMT
Location: http://foo.bar

{
    "error": "access_denied",
    "error_description": "The user denied access to your application"
}
```

after the included modification, it goes like this:

```
$ curl 'api.hfcit.dev/oauth/authorize?response_type=code&client_id=4a69dd44-fdf4-4c34-8fae-b8ef40818657&redirect_uri=http%3A%2F%2Ffoo.bar%2Fpath%3Fkey%3Dvalue&state=123'
HTTP/1.1 302 Found
Server: nginx/1.7.0
Content-Type: application/json
Transfer-Encoding: chunked
Connection: keep-alive
Cache-Control: no-cache
Date: Sun, 27 Apr 2014 18:01:33 GMT
Location: http://foo.bar/path?key=value&error=access_denied&error_description=The+user+denied+access+to+your+application
```

that is how we should handle it :)

@bshaffer WDYT?