Added
- Integrated the support for [native migrations](https://saffier.tarsild.io/migrations.md) with Saffier.
* This brings native generated migrations within Saffier under Alembic's package, allowing
a seemless integration and cross-compatibility with any framework using Saffier.
- Added new [DatabaseTestClient](https://saffier.tarsild.io/test-client.md) delegating the creating of the `test` database
for each connection string provided.
* No more needed to manually create two separate databases thanks to the client that does the
automatic management for you.