This pr adds support for foreign keys, table constraints in SQLite. They can only reference Primary keys of other tables and not Unique keys, since this would require changes in Quasi and I'm not sure how well this is supported in other dbs. I've tested migrations from existing schemas, which adds new foreign keys to existing Tables and it also works fine.

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• Bumped the version number
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• Update the Changelog.md file with a link to your PR
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