Create a C++ CDC connector

The cdc_connector.cpp should be expanded and incorporated into a minimal connector library.

The API it provides consists of the following actions.

• Connect to a MaxScale CDC service
• Authenticate and register as a listener for changes to a table
• Read data sent by MaxScale

The data reading function should return an object that represent a single change in data (either an INSERT, a DELETE or an UPDATE). The object should expose the names, types and values of each field in the changed row.