2.1.0

New features:

• Type-safe JSON serialisation via Deriving_Json: new modules Store_json, Ref_json and functor Column.Json in all backends, as alternatives to the Marshal-based Store, Ref and Column.Marshal. Persisted data is human-readable and stable across OCaml versions. Adds a dependency on js_of_ocaml (for the Deriving_Json runtime only).
• iter and fold added to the Polymorphic interface; iter_step/fold_step deprecated.
• iter_batch implemented for the SQLite and DBM backends.

Bug fixes:

• SQLite: keep a persistent database connection instead of open/close per operation.
• PostgreSQL: fix replace_if_exists, wrap modify_opt in a transaction, fix Functorial.length and Functorial.fold/Polymorphic.fold.
• DBM: replace the double-fork with Unix.create_process (OCaml 5 compatible).

Security:

• Validate table and store names in all backends to prevent SQL injection.

Other:

• Add a test suite for the three backends and a CI workflow.

This release is fully backward-compatible with 2.0.0 (additive API).