Merge pull request #11 from lopho/master

JUnit Test for world performers (simple)
check if EntitySystem wants to delete entites from itself, and delay the deletion to after processing.
World#deleteEntity: check deleted first, more likely to remove twice than add&remove.
removed blank lines
Merge pull request #12 from lopho/fixing-process

Fixing process
Rmmoved EntitySystem#isProcessing since it is essentially an internal state in a single-threaded framework.