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 )
@docteurklein It's there to catch if the argument is something else than "name" or "value". When you use a string instead of an array, it is automatically transform in a ['name' => '…'] array. Therefore checking if the argument name ("name" here) is correct does not really make sense.