Style: use of interface instead of class.
Code cleaning.
Formatting.
Started with Evaluator class based on plista data.

TODO: finish the LogGenerator class.
Merge branch 'master' of https://github.com/recommenders/plistarecs
LuceneRecommender: formatting and deleted threads.

Finished and tested (with small dataset) evaluator and generator.
Fixed issue #11: limit the number of items stored in memory.
Merge branch 'master' of https://github.com/recommenders/plistarecs