Spaces to tabs, refactoring and API changes

 - renamed the namespace for all services
 - path_localized() and url_localized() removed
 - replacing `url_generator` and providing transparent locale-aware
   url generation via path(), url() and other means
 - exporting $app['translator'] to make compatible with
   Silex\Provider\TranslationServiceProvider
Fix require definitions
Add README
Change Twig extension name