* add SocketSubscribe crossMargin (TOPIC: /contract/marginMode)
* add SocketSubscribe crossLeverage (Topic: /contract/crossLeverage)
* add DELETE /api/v1/orders/multi-cancel
* add GET /api/v2/position/getMarginMode
* add POST /api/v2/position/changeMarginMode
* add GET /api/v2/getCrossUserLeverage
* add POST /api/v2/changeCrossUserLeverage