Sync 0.3 branch #2382

Job	Run time
cargo bench	54s
cargo +stable build	45s
codegen	25s
cargo clippy	27s
cargo +beta build	42s
cargo +1.36 build (futures-{core, io, sink})	3m 5s
cargo +nightly build	42s
cargo doc	22s
cargo hack check --feature-powerset	2m 35s
cargo fmt	13s
cargo minimal-versions build	27s
cargo miri test	7m 32s
cargo build --target thumbv7m-none-eabi	32s
cargo test -Z sanitizer=address	2m 54s
cargo build --target thumbv6m-none-eabi	29s
cargo +1.56 build	1m 53s
cargo test (ubuntu-latest)	2m 56s
cargo test -Z sanitizer=memory	3m 51s
cargo test (macos-latest)	7m 54s
cargo test -Z sanitizer=thread	2m 17s
cargo test (windows-latest)	4m 9s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	3m 21s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	6m 13s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	6m 35s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	3m 30s
	1h 4m 43s

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