The One With SciKit APIs

LensKit 0.5.0 modifies the algorithm APIs to follow the SciKit design patterns instead of
our previous custom patterns. Highlights of this change:

• Algorithms are trained in-place — we no longer have distinct model objects.
• Model data is stored as attributes on the algorithm object that end in _.
• Instead of writing model = algo.train_model(ratings), call algo.fit(ratings).

We also have some new capabilities:

• Ben Frederickson's Implicit library

As always, install with

conda install -c lenskit lenskit