Connector plugins and toolkits for HStream IO.

Toolkits are libraries for developers to create new connector plugins, now we have implemented the java-toolkit, based on java-toolkit, you only need to implement a couple of interfaces to create a connector plugin instead of caring about offset, batch, protocol messages processing, etc.

Debezium is a great CDC tool for databases, we use debezium engine to synchronize data from databases, source-debezium is not a real connector plugin, it is the general database source library for building the real database connector plugins including source-mysql, source-postgresql, source-sqlserver, etc.

We use jdbc as a general interface to write data from HStreamDB streams to sink databases. like source-debezium, sink-jdbc is not an actual connector plugin either, we use sink-jdbc to build the database connectors including sink-mysql, sink-postgresql, etc.

sink-jdbc uses the UPSERT statement to implement INSERT and UPDATE for idempotence, so it can deal with the duplicated records caused by resending.