node http(s) server graceful shutdown

Adds a `shutdown(callback) to nodes http(s) servers. shutdown() will stop accepting new connections and waits until all requests are finished.
This is very similar to the node builtin close() function with the only difference that shutdown() destroys idle connections (e.g. keep alive connections) using a timeout (10 seconds as default) without data transfer.

Usage

`javascript
var enableGracefulShutdown = require('server-graceful-shutdown');

var server = http.createServer(function(req, res) {
// do stuff
});

server.listen(80);

// enhance server with a 'shutdown' function
enableGracefulShutdown(server);
// you can set the socket idle timeout using the second parameter
// e.g. enableGracefulShutdown(server, 5000);

// some time later...
server.shutdown(function() {
// all requests are finished
// we can
// process.exit()
// now
});
``