Fixes #32: Attach relationships to models in factory definitions

[axit-joost]

This PR will add the ability for the FactoryGenerator to render a relationship definition.

Instead of:

$factory->define(Person::class, function (Faker $faker) {
    return [
        'additionalName' => $faker->word,
        'address_id' => $faker->randomDigitNotNull,
        'familyName' => $faker->word,
        'givenName' => $faker->word,
    ];
});

It will now yield:

$factory->define(Person::class, function (Faker $faker) {
    return [
        'additionalName' => $faker->word,
        'address_id' => factory(App\PostalAddress::class),
        'familyName' => $faker->word,
        'givenName' => $faker->word,
    ];
});

Using the factory to create a Person will also yield the creation of a PostalAddress.

PR includes an updated fixture to allow the test suite to get green.

If there's anything that needs to be changed, please let me know.

Cheers!

[jasonmccreary]

Thanks for this. I am closing to make some small adjustments and will merge.