Merge pull request #51 from SgtCoDFish/master

#50: Add convenience Entity.getFor(Class<? extends Component>) method
Ups Libgdx version to 1.3.1
Adds PooledEngine.clearPools()
Adds benchmark
Update README.md
Fixes family filtering bug issue #56
Adds EntitySystem.setProcessing() method issue #55
Updates EngineTests for setProcessing.
Adds Engine.getSystems()
Fixes issue #44 (removing entities mid iteration)
Uses SnapshotArray to simplify EntityListener dispatch
Entity uses an unordered array of components issue #59
Adds EntityListeners on a per family basis
Adds test that iterates through family while changing family membership.
Ups Ashley version to 1.2.0 (pre release)
Ups version to 1.2.1 (after release)
Finally fixes horrible issue #44 (fingers crossed)
Adds missing @Test annotation
Delayed entity removal requests are processed after the next system finishes updating
Adds IntervalEntitySystem and IntervalIteratingEntitySystem issue #63
Renames new entity systems for simplicity
Adds test for issue #64
Fixes potential problem when removing entities from PooledEngine