ErrTooManyAffectedRows returned when store modifes too many rows.

Migrator defines generic interface for migrations.

MigratorFactory define method for migrations of store.

Store define generic interface for database with transaction support.

StoreFactory define interface of factory methods.

StoreTx define interface of transactional of store.

TxFunc define signature of callback used in tx block.

Txier define function to start tx block.