Add a short syntax to routing arguments

A string argument is now a `name` argument by default.

Instead of using :

    resources:
        edit:
            defaults:
                _resources:
                    entity:
                        …
                        arguments: [{name: foo}, {value: 5}, {name: bar}, {value: norf}]

You can now use the short syntax :

    arguments: [foo, {value: 5}, bar, {value: norf}]

`arguments: [id]` is now equivalent to `arguments: [{name: id}]`.

(Thanks to @PedroTroller )
He needs this method [here](https://github.com/KnpLabs/KnpRadBundle/pull/201/files#diff-1f706055bad5fd9fc278bc264970eda3R37) and [here](https://github.com/KnpLabs/KnpRadBundle/pull/201/files#diff-963fc3de858c6daf21b2c0849632ee16R38)