Updating to varnish 4.0.2 and more features

Added support for:
- websockets
  (https://www.varnish-cache.org/docs/4.0/users-guide/vcl-example-websockets.html)
- sorting the query arguments to improve hitratio
  (std.querysort(req.url))
- force refresh (http.Cache-Control=no-cache) using purge
- streaming for big files (beresp.do_stream = true)
- kind of stale-while-revalidate & grace
Merge pull request #3 from jnerin/master

Updating to varnish 4.0.2 and more features