Adding server side varnish purging.

Ban's are not scalable with the number of objects Huddler will need to support.
This commit adds server side varnish purging via the PURGE method.

/cc @loganlinn
Configuring logs to rotate.
Fixing unit tests.
Adding purge support on delete.
Cleaning up the hashing and purging in varnish.
Adding LRU_INTERVAL and SESS_WORKSPACE.
Only purge on update or delete.
Fixed and tested purges.
Removing Vary. It's not needed.
Adding Vary back in and testing variants just to be safe.
More testing. Only hash the URL.
Adding another acl for 192.*.
Merge pull request #15 from drsnyder/varnish-purge

Varnish purge support