Ability to specify cache time on get requests

[ghost]

Would be nice with an option to specify a cache option when setting a route

router.file(__dirname + '/static/404.html',{status:404, cacheMaxAge:60});
this would set the http header "cache-control" to "max-age=60" for 1 min client side cache

default should not set the http cache-control header (as it currently does)

[mafintosh]

closed with 66e2f52