Feature Request: Borrow less when possible.

[dscotese]

If Grid trading proceeds during down markets, the bot will use margin. If the grid trading generates enough profit, it can follow a procedure to reduce how much is being borrowed and save a little money:

1. Are there cryptos for which we have more than one buy? If so, the lower-priced buys can be cancelled.
2. How much USD is available? (the bot tracks this by keeping track of its own buys, though there may be better ways... future issue?)
3. The bot could have a setting to maintain some level of available cash, and when the answer to the question above exceeds that, then some of the positions held can be settled with the extra cash. The least volatile asset seems to me to be the best target for such settlement but I'd have to guess which one that is, and that could change over time anyway.