Better iou condensing algorithm

A much better algorithm for condensing IOUs into fewer transfers

New algorithm goes like this:
1. Calculate universal balances. AKA Jack is owed $34, Sam owes $12,
Roy owes $66, Kyle is owed $44
2. Find person who owes the most, aka Roy
3. Generate IOUs where Roy pays all people who are owed (Jack, Kyle)
4. Create remaining IOUs where all other people who owe just pay Roy
their balances