Order querying improvements

get_all_orders() is now configurable with its days_back parameter - it will now return only as many (market) days as are requested. The default behavior is to get all orders, so be sure to limit your calls if possible to get a performance boost. get_recent_orders exists as a convenience method to get orders of all types from the last few days, and defaults to 2 days of data.

An issue was also fixed where get_order would not return older orders. get_order should now return the order regardless of how long ago it was submitted.