Missing Isolated Margin borrow calls

[pr0logas]

https://docs.kucoin.com/#isolated-margin-borrowing

Currently only cross margin borrow calls are supported which is default method by Kucoin:

    def create_borrow_order(self, currency, order_type, size, **kwargs):
        """
        https://docs.kucoin.com/#post-borrow-order
        :param currency: Currency to Borrow (Mandatory)
        :type: str
        :param order_type: Type: FOK, IOC (Mandatory)
        :type: str
        :param size: Total size (Mandatory)
        :type: float
        :param kwargs: [Optional] maxRate, term
        :return:
        {
            "orderId": "a2111213",
            "currency": "USDT"
        }
        """
        params = {
            'currency': currency,
            'type': order_type,
            'size': size,
        }
        if kwargs:
            params.update(kwargs)
        return self._request('POST', '/api/v1/margin/borrow', params=params)