add brotli compression support

[gruns]

brotli is widely supported in browsers (https://caniuse.com/brotli) and enough superior to gzip to use it over gzip when supported

see https://docs.nginx.com/nginx/admin-guide/dynamic-modules/brotli/ and http://wiki.centos-webpanel.com/enabling-brotli-compression-on-nginx

there has to be some way to add brotli support without nginx plus.. but if nginx plus keeps being an impediment to our various usage, ie death by a thousand cuts, perhaps its worth migrating to another http server in the future (😢)

[gruns]

see #22 for the greater context

[gruns]

🎉 @enolal826