Simple in-memory transactional key-value store.

• Supports get, set, delete, count, begin, rollback, commit operations.
• Supports nested transactions.
• Commit/rollback operations apply changes from the last transaction.
• Parallel/concurrent transactions are not supported.
• Not thread-safe!

Has 2 implementations:

1. TkvsSingleMap.kt
   Implementation with single map, change logs, and value counters cache for O(1) computational complexity of count operation.
2. TkvsStackOfMaps.kt
   Implementation based on stack of maps.

Unit tests: TransactionalKeyValueStoreTestBase.kt

A built jar is available in bin/tkvs.jar.
Run it with java -jar bin/tkvs.jar for an interactive console (uses "single map" implementation).
In the console, type h or help to see available commands.