Exq 0.6.4

• Support url method for redis url
• Create Exq.Api for web stats and move out of Enqueuer
• mode option for starting entire system, enqueuer, or api.
• Centralize config defaults

Use Redix instead of eredis. Worker Supervision.

• Use Redix instead of eredis.
• Worker Supervision.
• Fix mix task.
• Worker to perform retry_fail job