Add multi-symbol handling and prevent day trading

[Flawlesssharky6]

You can now trade as many symbols as you want by adding or removing the symbols to the list "symbols". Ensure you are doing that on lines 111 and 121 (you should change it on line 26 to be safe but it doesn't matter).

You can also change self.sleeptime to whatever you want and not worry about day trading. My testing found that 24H is still one of the better general self.sleeptime, but knowing you can't day trade is still nice. If you want to day trade you can just comment out lines 68-72, 88, and 102 (the most important lines are 70-72).