0.20.1

• Drain in-flight requests until graceful_timeout on shutdown.
• Implement the Path Send extension (http.response.pathsend), streaming a file the app names by path as the response body on any HTTP version.
• Implement the Zero Copy Send extension (http.response.zerocopysend) with a real os.sendfile over a TCP HTTP/1.1 socket. It is advertised only where it can really be zero copy - HTTP/2, HTTP/3, userspace TLS and UNIX-domain-socket connections are not offered it rather than silently reading and sending (os.sendfile is not portable over a UNIX socket). Path send now routes through the same path, so it too is os.sendfile on TCP HTTP/1.1.
• Add a use_ktls config flag that binds TLS to the accepted socket and asks OpenSSL to enable kernel TLS, so os.sendfile (zerocopysend and pathsend) still works over a TLS HTTP/1.1 connection. It takes effect only on Linux with an OpenSSL that supports kTLS; elsewhere TLS is still served in userspace and the socket path falls back to reading and encrypting through the stream.