Input format for binary forecasts and point predictions

[nikosbosse]

We need to have a clear interface for binary and point forecasts. The problem is that the distinction is not always self-evident: A forecast of 0.8 for a true_value of 1 could either be a point forecast or a binary forecast. They would need different scores though.

In order to allow for commenting, I created a Google doc for the discussion: https://docs.google.com/document/d/1KBmgYro2uuKZJzlOznPuD9gvRsTf4cnPvqnfJHpdOwM/edit