modified WorkerQueueInterface; queue now returns workers in LIFO order if priority of workers is equal; removed Zend's priority queue
Merge branch 'worker-queue-lifo-order'

Conflicts:
	README.md
	composer.json
	composer.lock
	src/PHPExtra/EventManager/EventManager.php
	src/PHPExtra/EventManager/Worker/AbstractWorkerQueue.php
	src/PHPExtra/EventManager/Worker/WorkerQueue.php
	src/PHPExtra/EventManager/Worker/WorkerQueueInterface.php
modified WorkerQueueInterface; queue now returns workers in LIFO order if priority of workers is equal; removed Zend's priority queue