How do I get a list of open positions via the API? That is, suppose I BUY two BTC-USD at (say) 9500ドル and 9600,ドル with sizes of 0.6 and 1.2 respectively. How would I a list of these open positions? The fill method gets me the full history, but it doesn't tell me which positions are still open. I need a quick way of making sure my app is in sync with the exchange... Thanks