Leverage browser caching by specifying max-age

I've noticed that adding a `max-age` value to `cache-control` header results in a much better real-life behaviour and yields a better results in speed test analysing tools such as Google's [PageSpeed Insights](https://developers.google.com/speed/pagespeed/insights/) or [Pingdom Tools](http://tools.pingdom.com/fpt/).

Even though requests to cached resources are quickly responded with `304`, adding a `max-age` value results in **less requests** being made to the server.

Ideally we would need to have a separate `browser.axAge` cache option, but it somehow seems logical to assimilate it with `content.maxAge`...

What do you think?