Support for ICanBoogie's auto-config

The package supports the auto-config feature of the framework ICanBoogie and provides
the following:

• A synthesizer for the activerecord_connections config, created from the activerecord
  fragments.
• A lazy getter for the ICanBoogie\Core::$connections property, that return a Connections
  instance created with the activerecord_connections config.
• A lazy getter for the ICanBoogie\Core::$db property, that return the connection named
  primary from the ICanBoogie\Core::$connections property.