Add support for "Expect: 100-continue" header #1869

Job	Run time
Docs	38s
build_versions (stable)	14s
cargo-deny (aarch64-apple-ios)	52s
build_versions (beta)	20s
cargo-deny (aarch64-linux-android)	19s
Test	1m 3s
Lint	1m 2s
build_versions (1.61.0)	30s
cargo-deny (i686-pc-windows-gnu)	21s
Test (json)	57s
cargo-deny (i686-pc-windows-msvc)	46s
Test (charset)	51s
Test (cookies)	56s
cargo-deny (i686-unknown-linux-gnu)	20s
Test (socks-proxy)	45s
cargo-deny (wasm32-unknown-unknown)	19s
Test (native-certs)	45s
cargo-deny (x86_64-apple-darwin)	21s
Test (gzip)	55s
cargo-deny (x86_64-apple-ios)	19s
Test (brotli)	54s
cargo-deny (x86_64-pc-windows-gnu)	20s
Test (http-crate)	1m 50s
cargo-deny (x86_64-pc-windows-msvc)	21s
Test (http-interop)	1m 3s
cargo-deny (x86_64-unknown-linux-gnu)	25s
Test (http-crate http-interop)	1m 34s
cargo-deny (x86_64-unknown-redox)	22s
Test (tls)	48s
Test (tls, json)	49s
Test (tls, charset)	58s
Test (tls, cookies)	57s
Test (tls, socks-proxy)	56s
Test (tls, native-certs)	46s
Test (tls, gzip)	55s
Test (tls, brotli)	51s
Test (tls, http-crate)	53s
Test (tls, http-interop)	53s
Test (tls, http-crate http-interop)	58s
Test (native-tls)	50s
Test (native-tls, json)	47s
Test (native-tls, charset)	51s
Test (native-tls, cookies)	55s
Test (native-tls, socks-proxy)	47s
Test (native-tls, native-certs)	50s
Test (native-tls, gzip)	1m 13s
Test (native-tls, brotli)	58s
Test (native-tls, http-crate)	51s
Test (native-tls, http-interop)	51s
Test (native-tls, http-crate http-interop)	1m 1s
	39m 0s

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