Added max_age header

[mehigh]

@westonruter

When using this on a project, just with the Expire header, Google Page Speed was complaining of not leveraging browser caching.

"Leverage browser caching You have enabled browser caching. Learn more about browser caching recommendations."

With this patch, the browser caching is used properly, and makes the caching test pass.

I've guided myself by this when making these amendments: https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching#cache-control

[mehigh]

I'll make Travis happy some other day. It's pretty much coding style issues he reported, not specific to the code I pushed, but I'll get them tidy before bumping someone to merge this into dev.

[westonruter]

@mehigh good catch!