Add a Symfony2 bundle to integrate with the Symfony2 Dependency Injection Container

By having the bootstrap managed by the DIC, it becomes a lot easier to use.
Also, the XML file is way more maintainable than the annoying manual
construction of the object graph.

Sample usage:

    $collectionBuilder = $container->get('simple_php_easy_plus.number_collection_builder');
    $engine = $container->get('simple_php_easy_plus.engine');
    $runner = $container->get('simple_php_easy_plus.runner');

    $collectionBuilder->add('1');
    $collectionBuilder->add('2');

    $calcul = new Calcul($engine, $collectionBuilder->resolve());
    $runner->run($calcul);

    $value = $calcul->getResult()->getValue();
Merge branch 'number-collection-builder' into symfony-bundle

* number-collection-builder:
  Mock SimpleNumberStringParserInterface instead of implementation
Move extension creation in extension test
Change number_collection_builder to prototype scope

This ensures that a new builder is created every time. Thanks to
@magnusnordlander for pointing this out.
Merge remote-tracking branch 'igorw/symfony-bundle'

Conflicts:
	composer.json
Update dependencies