Adds missing varnish 3.0 syntax

* Adds highlighting for purge and ban function names (varnish 3.0)
* Adds hit_for_pass mode/state
* Highlight "week" duration e.g. set beresp.ttl = 1w;
* Highlight bool values e.g. set beresp.do_gzip = true;
* Adds req.esi_level property