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## Order book trading

* Added `POST /api/v5/trade/mass-cancel` to cancel all open orders for a given
  instrument family in a single request, primarily for options market makers.
* The `attachAlgoOrds` parameter on `POST /api/v5/trade/order` now supports
  attaching multiple take-profit / stop-loss brackets to a single order.
* Added the `linkedAlgoOrd` field to `GET /api/v5/trade/order` responses,
  surfacing the algo order id linked to a placed order.