Fix JavaDoc build error
Fix compiler warnings in lenskit-data-structures
Drop use of SolverException in lenskit-core
Drop use of SolverException in non-core modules
Clean up warnings in lenskit-core

Lots of these are fast collection warnings. Some are serial version UIDs, and a smattering of other warnings.
Fix KNN and slope-one warnings
Use non-raw types for Metric uses
Clean up more lenskit-eval warnings
Clean up warning in ML100K
Clean up lenskit-cli compiler warnings

- deprecated isCompressed() method
- strange gyrations with Ant project targets
Remove unneeded build system elements
apply base plugin in root project
Add Plus event (#517)

- Plus event interface
- SimplePlus implementation and factories
- Tests for the factories
Add EventBuilder abstraction
Add UnaryEventBuilder abstraction for unary events
Add PlusBuilder and a test class