Prefixed Stripe PHP library for PublishPress

Prefixed version of stripe/stripe-php. Namespace Stripe becomes PublishPress\Stripe.

How to update the prefixed library

1. Change the pinned upstream version in require-dev (stripe/stripe-php) to the target fixed version.
2. Set version to that upstream version plus the next fourth digit (20.3.1 becomes 20.3.1.1 for the first prefixed build).
3. Run composer update. Strauss prefixes into lib/; the generator refreshes include.php and VersionLoader.php.
4. Run composer test:unit, then composer test:integration.
5. Review the prefixed code in lib/ by hand and commit.
6. Create a GitHub release named with the four-digit version so Packagist sees the tag.

Then run composer update in the plugins that consume the package.