Add support for custom host

[macmichael01]

Currently, I can serve content on a custom port:

  let port = 1234;
  let server = gls.static(config.content, port);
  server.start();

It would be awesome if I could serve on a custom host too:

  let port = 1233;
  let host = '192.168.0.5';
  let server = gls.static(config.content, host, port);
  server.start();