🏗️ Dry run: add redis streams support

[Terkwood]

Description

Test run at solving redis-rs#162. Merges https://github.com/grippy/redis-streams-rs into redis-rs.

We're mainly opening this PR within a forked repo so that we can easily view the changes over the web. We plan to eventually raise a PR against the main redis-rs repo, once this work looks reasonably complete.

If anyone feels like providing feedback at this stage, you are encouraged to do so!

Tasks

• provide cargo feature for streams
• carry over the integration test from redis-streams-rs, using REDISRS_SERVER_TYPE correctly
• pass REDISRS_SERVER_TYPE=unix cargo test --all-features -- --skip test_cluster
• pass REDISRS_SERVER_TYPE=tcp RUST_TEST_THREADS=1 cargo test --all-features -- --nocapture --skip test_cluster
• pass cargo test --doc
• position these changes logically w.r.t. the existing code base
• transfer all commands
• transfer all stream types
• satisfy all doc lints
• make a final pass on docs for commands and make sure they contain info from redis docs
• make a final pass on docs for types and make sure they contain info from redis docs
• update README

[Terkwood]

This looks like it's ready to be raised against the main repo.

[Terkwood]

See redis-rs#319.