Data types in event.h

Data types in the error information API section for naming error types and defining the structure that holds error information.

All errors have an associated mmsync_error_t structure, which is referenced by the data field in the mmsync_event_t structure returned for MMSYNC_EVENT_SYNC_ERROR events. The mmsync_error_t structure contains the error type, synchronization operation ID, and other error information such as the ID of folder where the error occurred.