access header
$ curl -I https://api.github.com/users/octocat/orgs
> HTTP/2 200
> Server: nginx
> Date: Fri, 12 Oct 2012 23:33:14 GMT
> Content-Type: application/json; charset=utf-8
> ETag: "a00049ba79152d03380c34652f2cb612"
> X-GitHub-Media-Type: github.v3
> X-RateLimit-Limit: 5000
> X-RateLimit-Remaining: 4987
> X-RateLimit-Reset: 1350085394
> Content-Length: 5
> Cache-Control: max-age=0, private, must-revalidate
> X-Content-Type-Options: nosniff