Add support for permessage-deflate WebSocket extension

[segfault87]

PR Type

Feature

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

This PR implements DEFLATE compression (specifically permessage-deflate extension which defined at RFC 7692) support for WebSocket.
The whole feature is flagged behind compress-ws-deflate feature.
Currently, flate2 requires zlib for certain feature required by permessage-deflate extension. Therefore using this feature will introduce extra zlib dependency.

Also, Codec has been modified to split into Encoder and Decoder as there are some cases when encoding and decoding take place in different producer/consumers. Still its interface is unmodified in order to prevent API compatibility breakage.

A PR counterpart on actix-ws will follow.

[segfault87]

On the idea of implementing the extension outside of actix-http, I elaborated a bit at this comment: actix/actix-extras#479 (comment)

[asonix]

There's a lot here but I think overall this looks good :) It's unfortunate that this is a breaking change to the public API in a few places. I'm not sure what the plan is for a new major version of actix-http/actix-web although I assume there's no immediate plans for such a release.

[segfault87]

@robjtede Could you have a look at this?