middleware to compress response body with gzip or deflate

 Plack::Middleware::Deflater is a middleware to encode your response body in
 gzip or deflate, based on the Accept-Encoding HTTP request header. While
 saving a little bandwidth it will increase the Plack server load, so ideally
 you should handle this on the frontend reverse proxy servers.
 .
 This middleware removes Content-Length and streams encoded content, which
 means the server should support HTTP/1.1 chunked response or downgrade to
 HTTP/1.0 and close the connection.