Stabilize some of the foundational types in a separate crate

[dtolnay]

The current situation is:

• Reqwest would like to release a stable version.
• Currently reqwest re-exports the Method, StatusCode, and HttpVersion types from hyper, so it couldn't be stable until hyper is stable.
• Stable hyper is waiting on stable tokio.
• Stable tokio is not imminent.

Let's extract these foundational types into a separate crate that we can stabilize sooner than all of hyper.

[theduke]

I would suggest to try and use the http crate name for this.

It already exists, https://crates.io/crates/http , but the owner could hopefully persuaded to give it up.

[seanmonstar]

Yes, we would. We've been in contact with the owner, he specifically reserved it for just such an effort.

However, it's probably a bit ambitious to stabilize an http crate super quickly, so for reqwest, it will likely just define its own types, and we'll hope that an eventual http crate mirrors what it has.

[jimmycuadra]

Possible dupe of #894?

[seanmonstar]

Yes, dupe, so I'm going to close. There's issues opened in reqwest crate about implementing those primitives there.