Functions returning multiple values should probably be returning objects

[ghost]

Looking at arbitrer.py, it seems there is still some encapsulation and abstraction to be done. I don't personally like it when a function returns more than one value, and here we have functions returning as many as six values. It's very easy to mix up return values, and it's very hard to update anything that uses those functions if those functions change.

I propose we create a class to encapsulate those values, and perhaps move some of Arbitrer's functionality into that class. This could also facilitate using other currencies as "pivot" currencies, or at the very least aid in finding arbitrage chains that include links without USD as one of the currencies involved. (I.e., inter-crypto arbitrage.)