Bug fixes, major logic improvement.

Logic improvement:
— The depth penalty now checks for the distance between the buy price
at depth and the sell price at depth, thus now accounting for both
margin and depth in the penalty.

Bug fixes:
— Fixed a bug in calculating performance, where the balance from the
last round wasn’t properly kept.
— Fixed a bug in generating orders, where it was possible for an order
under the minimum size.
— Fixed a bug where a stacked chain of recursive calls to the trading
engine was generated (errrr bad times).