Make possible to set `client_order_id`

[Bi0max]

As it seems from the current code, it's not possible to set client_order_id:

pub fn limit_sell(&self, market_pair: &str, size: &str, price: &str, time_in_force: TimeInForce, post_only: bool)

Without it, it's harder to track orders.

[notdanilo]

This issue depends on nash-io/openlimits#148