Redis 2.6 conf updates

Update attribute references to` hash_max_zipmap_*` to be `hash_max_ziplist_*` and update the default template.

Remove `vm_*` attribute references from README and defaults (these have already been excluded in the template).

An example of a current (2.6) `redis.conf` file can be found at https://raw.github.com/antirez/redis/2.6/redis.conf