actix-web-lab: v0.17.0

• Add sse::Sse::from_stream() constructor.
• Add sse::Data::new_json() constructor.
• Rename sse::{sse => channel}().
• Rename sse::{SseData => Data}().
• Rename sse::{SseMessage => Event}().
• Rename sse::{SseSendError => SendError}.
• Rename sse::{SseTrySendError => TrySendError}.
• Removed extract::BodyHash and associated types; promoted to actix-hash crate.
• Removed extract::BodyHmac and associated types; prefer RequestSignatureScheme + RequestSignature. See body_hmac in examples folder.
• Removed header::Hsts alias; use header::StrictTransportSecurity.