title: Sequelize: insert in bulk
body: <p>I'm using Node.js, MySQL and Sequelize. I'd like to insert some 10k rows into a table at once. The table has custom <code>primaryKey</code> field, that is being set manually. The data are downloaded from web and are overlapping.</p>
  
  <p>I'd like to have a version of <code>bulkCreate</code> that wouldn't fail if any of the rows in data have unique keys that are already present in the table. Such kind of things is done in MySQL via <code>INSERT ... ON DUPLICATE KEY UPDATE</code> construct.</p>
  
  <p>How do I do it in Sequelize?</p>