Don't export Header struct #1712

Job	Run time
Docs	28s
cargo-deny (aarch64-apple-ios)	22s
Test	10s
Lint	21s
cargo-deny (aarch64-linux-android)	20s
Test (json)	9s
cargo-deny (i686-pc-windows-gnu)	20s
Test (charset)	29s
cargo-deny (i686-pc-windows-msvc)	22s
Test (cookies)	33s
cargo-deny (i686-unknown-linux-gnu)	18s
Test (socks-proxy)	1s
cargo-deny (wasm32-unknown-unknown)	19s
Test (native-certs)	10s
cargo-deny (x86_64-apple-darwin)	18s
Test (gzip)	34s
cargo-deny (x86_64-apple-ios)	19s
cargo-deny (x86_64-pc-windows-gnu)	19s
Test (brotli)	34s
cargo-deny (x86_64-pc-windows-msvc)	24s
Test (http-interop)	13s
cargo-deny (x86_64-unknown-linux-gnu)	21s
Test (tls)	2s
cargo-deny (x86_64-unknown-redox)	18s
Test (tls, json)	1s
Test (tls, charset)	1s
Test (tls, cookies)	1s
Test (tls, socks-proxy)	1s
Test (tls, native-certs)	1s
Test (tls, gzip)	1s
Test (tls, brotli)	1s
Test (tls, http-interop)	1s
Test (native-tls)	8s
Test (native-tls, json)	7s
Test (native-tls, charset)	8s
Test (native-tls, cookies)	9s
Test (native-tls, socks-proxy)	2s
Test (native-tls, native-certs)	3s
Test (native-tls, gzip)	4s
Test (native-tls, brotli)	8s
Test (native-tls, http-interop)	6s
	8m 47s

Provide feedback