HTTP response freshness testing
Check freshness of req and res headers.
When the cache is "fresh" true is returned, otherwise false is returned to indicate that the cache is now stale.
var req = { 'if-none-match': 'tobi' };
var res = { 'etag': 'luna' };
fresh(req, res);
// => false
var req = { 'if-none-match': 'tobi' };
var res = { 'etag': 'tobi' };
fresh(req, res);
// => true$ npm install fresh