NoCache middleware - prevents proxies/clients from caching content.

Prevents proxies/clients from caching routes. Pretty simple. Based on standardised HTTP headers and nginx/HAProxy headers as per http://wiki.nginx.org/HttpProxyModule

I use it to ensure things don't get cached by clients or internal proxy caches, both in production and development.

It sets:

```sh
Cache-Control: "no-cache, private, max-age=0"
Expires: Thu, 01 Jan 1970 00:00:00 UTC
X-Accel-Expires: 0
```