Implement purging of queues

[mathieupinet]

Is there a plan to have support for the PurgeQueue() SQS API call to delete all messages in a queue?

[sjparkinson]

Clearing / purging a queue seems to be a generally supported feature for messaging systems.

I'm up for implementing this. Initial thoughts:

• Add public function purge(); to AdapterInterface
• Add public function purge(); to ProducterInterface
• Add an UnsupportedOperationException for adapters that may not support this feature