Add link to flex library

### What is the problem / feature ?

I have been writing a library to do swagger schema validation against arbitrary request/response objects and I just got to the point where I think this library can be useful to others.

```
   >>> import requests
   >>> from flex.core import load, ResponseValidator
   >>> schema = load("path/to/schema.yaml")
   >>> validator = ResponseValidator(schema)
   >>> response = requests.get('http://www.example.com/api/')
   >>> validator(response)
   ValueError: Invalid
   'response':
       - 'Request status code was not found in the known response codes.  Got `301`: Expected one of: `[200]`'
```

### How did it get implemented ?

- Parsing and validation of swagger 2.0 schemas
- Code to normalize responses from the `requests` library into an internal request/response object.
- Validation of request/response objects against a swagger schema.

### How can someone test / see it ?

Documentation provides code examples.

*Here is a cute animal picture for your troubles...*

![cute-raccoon-image-05](https://cloud.githubusercontent.com/assets/824194/4894603/67452d9c-63d6-11e4-97e1-323a2996072b.jpg)