Add. Custom exceptions for Connector and DataLoader classes.
Add. Custom exceptions for Connector and DataLoader classes.

wikimedia/analytics-user-metrics,wikimedia/analytics-user-metrics,wikimedia/user_metrics,wikimedia/user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/user_metrics,rfaulkner/wikipedia_user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/analytics-user-metrics