Upgrade to silex 1.1
Update composer.json

Add twig-bridge to use the UrlGenerator service
Update form demo

* extract the message in a separate template
* write the required javascript
* use the UrlGenerator
Update README.md

Decided to improve my README a bit after reading http://williamdurand.fr/2013/07/04/on-open-sourcing-libraries/

* add a short project description
* add requirements and license section