Merge pull request #6 from lopho/master

small bag perfomance improvements and documentation
World#notifySystems & World#notifyManagers now iterate over the bags array instead of using Bag#get(int), removing overhead from calling the method every iteration.
removed check calls from process except added, as the checks were called directly upon change of the entity.
removed corresponding bags as well. World#deleteEntity(Entity) now checks added if entity was just added, preventing the add, instead of adding & deleting.
added benchmarks to tests
Merge pull request #8 from lopho/world-performance

World performance
unit test for world performers