[WIP][Routing] Extended Expression Language in a routing component

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | none
| License       | MIT
| Doc PR        | not yet


- [ ] add tests
- [ ] add docs
- [x] gather feedback for my changes

A new expression language engine in a routing component can't extended with new custom functions, in my project i need custom function in a route condition.

with this patch and a custom compilerpass in my bundle i can added my custom function (version_compare of php).
this feature work with symfony/routing >= 2.4
```php
class OverrideServiceCompilerPass implements CompilerPassInterface
{
    public function process(ContainerBuilder $container){

        
        $definition = $container->getDefinition('router.default');

        $definition->addMethodCall('setExpressionLanguage',array(new Reference('examplebundle.routing_expression_language')));

    }
} 
```
a code of examplebundle.routing_expression_language is here:
```php
class NewExpressionLanguage extends ExpressionLanguage
{

    protected function registerFunctions()
    {
        parent::registerFunctions();

        $this->register('compare', function ($version1, $version2, $operator) {
            return sprintf('version_compare(%s, %s, %s)', $version1, $version2, $operator);
        }, function (array $values, $version1, $version2, $operator) {
            return version_compare($version1, $version2, $operator);
        });
    }

}
```