Bankroll Unrolled

Bankroll has now been split up into several projects with better separation of responsibilities, making it easier for other projects to build on top of pieces of bankroll without necessarily incorporating the whole monolith.

Development of new brokerages is also simplified: just build according to the interfaces in the bankroll-broker library, and make sure the new brokerage gets imported at runtime! Nothing needs to be added into the main project unless you would like to upstream your implementation.