Support SQLite changesets as a change mechanism

[otoolep]

Instead of writing directly to the database, perhaps something like this;

• Received SQL statement on the /db/execute endpoint.
• start a transaction on the rw connection to the database
• start a session, and apply the SQL statement as changeset.
• record the changeset
• rollback the transaction
• encapsulate the changeset bytes in a Raft log, and send it through the Raft consensus system as usual
• each node gets the Raft log entry, recognizes it's a changeset, and applies it.

Boom, rqlite can handle non-deterministic change. No more concerns about RANDOM, TIMESTAMP, and AUTOINCREMENT.

[otoolep]

This might be useful, as mattn/sqlite doesn't have direct support:

https://github.com/crawshaw/sqlite