Transactions

[marvin-j97]

We should have all the pieces to get transactions working:

• Snapshots achieved by MVCC
• Atomicity achieved by Batch

[marvin-j97]

Possible API

use fjall::TxKeyspace;

let keyspace = TxKeyspace::open( ... )?;
let items = keyspace.open_partition( ... )?;

let tx = keyspace.transaction();
tx.get(&items, key)?;
tx.insert(&items, newkey, newvalue);
tx.commit()?;

[marvin-j97]

Single-writer transactions will land in 1.1.0