Using compression based on Accept-Encoding

[wkhere]

Hi!

I am not sure if you intend to use this library only by a very specific user agent, but if you think of this middleware as of general purpose, there is this concern: user agent can set his preference in the Accept-Encoding header and the server should respect that; so, based on the header value, your middleware might skip compression and return the original content.

The rules are described in the RFC: https://rfc-editor.org/rfc/rfc7231#section-5.3.4