code: function define(type, Model) {
    if (arguments.length === 1) {
      Model = type;
      type = Model.prototype.__type || Model.modelName;
    }
  
    var factory = new Factory(Model);
    factories.set(type, factory)
  
    return factory;
  }
docs: Define a factory.
  
  @param {String} Type [optional]
  @param {Function} Seed model
  @api public