Option to serve compressed responses

[Lusitaniae]

I'm currently using fluentd to generate a giant amount of metrics which have already passed 50Mb response sizes in some of our nodes

I can bump limits and timeouts on the scraping side of things, but compressing the response would probably be very useful here!

$ curl -s http://node1:9106/metrics | wc -c
37420840
$ curl -s http://node1:9106/metrics | gzip -c | wc -c
1877477