Initial start on packed rating DAO
Add Cursors.concat

This implements Cursors.concat to concatenate cursors.
Implement missing pieces of binary DAO.
Implement packing in the evaluator
Use fast iteration over user histories
Logging speedups and improvements
Pack first to temporary file
Invoke default target from eval CLI
Add fast-path dot product
Deprecate & warn on CSV caching
Fix level config in logging
Fix erroneous binary DAO logging
Delete old soft provider
Boxing and other minor changes
Make log colors conditional
Make binary user histories fast-iterable
Reduce memory churning in item-item scoring
Implement itemwise context builder (#481)

This creates an item-by-item (rather than user-by-user) build context
builder to speed up item-item model builds.
Merge branch 'master' into feature/elehack-binpack