Starts an embeded nginx server where nginx-clojure module has been built into, e.g.
(1) Starts it with ring handler and an options map
 (run-server my-app {:port 8080})

(2) Starts it with a nginx.conf file
 (run-server "/my-dir/nginx.conf")

(3) Starts it with a given work dir
 (binding [*nginx-work-dir* my-work-dir]
   (run-server ...))