GZip client side middleware

[agourlay]

Currently the GZip middleware is only for server side.

The client could either reuse the server side middleware or just the compression logic added to a client side middleware.

Discussed on Gitter https://gitter.im/http4s/http4s?at=599aef13c101bc4e3a3f7b71

[agourlay]

FYI I am currently working on this

[rossabaker]

Which version are you targeting?

• If it's 0.18, cool.
• If it's 0.16 or 0.17 and you're only adding signatures, cool.
• If it's 0.16 or 0.17 and it needs to change any signatures, let's plan, because I'm about to cut RCs.

[agourlay]

I am gonna go for 0.18 to get complete freedom

[rossabaker]

#1373 was accidentally closed. That's a good starting point if anyone wants to pick this up and finish it.

[agourlay]

fixed by #2673