Add support for installing Pest into a Lumen application

[michaeldyrynda]

This entails creating Laravel and Lumen-specific stubs, and ensuring that the appropriate stubs are copied as part of the pest install.

The stubs/Lumen/Pest.php file needs to be updated before this can be merged

As uses(TestCase::class) has no effect without the call to ->in(), so tests won't actually work in a Lumen application because there is no namespace to load from.

Adding a call to uses(TestCase::class) in a test file itself does work, so it's possible to use Pest with Lumen, but will need the manual call in each test file at this stage.

[owenvoke]

Can you not use uses(TestCase::class)->in(__DIR__)?

[michaeldyrynda]

So you can!

[nunomaduro]

Thanks @michaeldyrynda !