Allow shorting of hard-to-borrow stocks

Most brokers offer shorting of easy-to-borrow stocks for free (same as Alpaca), and hard-to-borrow stocks are offered for a borrow fee (typically 1-5% annualized depending on the stock). Alpaca currently doesn't allow shorting hard-to-borrow stocks at all, meaning most long/short algorithms can't be run on Alpaca. Please add this feature! (And it will be a good source of revenue for Alpaca too!)