Merge pull request #28 from wajam/clement-delayed-tasks

Add support for delayed tasks in MemoryQueue
Merge pull request #29 from wajam/clement-delayed-tasks

Index delayed tasks by unique key
Max task retry
Fix retry unit tests

Random is not implicit anymore in SPNL Task, so it must now be passed explecitly...
Merge pull request #30 from wajam/manu-max-retry

Max task retry
Introduction of a formal QueueFactory trait
Merge pull request #31 from wajam/manu-queue-factory

Introduction of a formal QueueFactory trait
Merge branch 'master' into clement-delayed-tasks

Conflicts:
	bwl-core/src/main/scala/com/wajam/bwl/Bwl.scala
	bwl-core/src/main/scala/com/wajam/bwl/queue/log/LogQueue.scala
	bwl-core/src/main/scala/com/wajam/bwl/queue/memory/MemoryQueue.scala