* delay() can return milliseconds to delay sending next request.

wrk 4.0.0

 * The wrk global variable is the only global defined by default.
 * wrk.init() calls the global init(), remove calls to wrk.init().
 * Add wrk.lookup(host, port) and wrk.connect(addr) functions.
 * Add setup phase that calls the global setup() for each thread.
 * Allow assignment to thread.addr to specify the server address.
 * Add thread:set(name, value), thread:get(name), and thread:stop().
 * Record latency for every request instead of random samples.
 * Latency and requests in done() are now callable, not indexable.
 * Only record timeouts when a response is actually received.
 * Remove calibration phase and record rate at fixed interval.
 * Improve correction of coordinated omission.