v1.16

• Moved wildcard purges to a background job, managed by Qless. This means that wildcard purges will always return 200, regardless of whether there was anything to purge or not.
• Wildcard purges now attempt to use a Redis slave for SCAN commands, if available.
• Qless jobs are now tagged with their type, as purge, revalidate or collect_entity. This helps tracking.
• Qless jobs now have different priorities: collect_entity is highest, revalidate second, and purge lowest.
• max_stale config setting now ignores response headers in deciding if it's ok to serve stale (essentially it overrides). Though they are still honoured when the client issues a Cache-Control: max-stale=n header.
• Background revalidation now has SSL support.