Export Sqids from sqids module

The previous code did not export the Sqids class leading to private
import usage warnings when using `from sqids import Sqids`.
One could work around it by using `from sqids.sqids import Sqids`.
This workaround is now no longer necessary.

Author: Popkornium18

sqids/__init__.py

@@ -1 +1,3 @@
-from .sqids import Sqids  # noqa: F401
+from .sqids import Sqids
+
+__all__ = ["Sqids"]