Release 0.6.1

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Build succeeded:

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• CI (1.46.0, --features=async-tokio, x86_64-unknown-linux-gnu)
• CI (1.46.0, --features=mio-evented, x86_64-unknown-linux-gnu)
• CI (1.46.0, x86_64-apple-darwin)
• CI (1.46.0, x86_64-unknown-linux-gnu)
• CI (stable, aarch64-unknown-linux-gnu)
• CI (stable, arm-unknown-linux-gnueabi)
• CI (stable, armv7-unknown-linux-gnueabihf)
• CI (stable, --features=async-tokio, x86_64-unknown-linux-gnu)
• CI (stable, --features=mio-evented, x86_64-unknown-linux-gnu)
• CI (stable, i686-unknown-linux-gnu)
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• CI (stable, mips64-unknown-linux-gnuabi64)
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• CI (stable, mips-unknown-linux-gnu)
• CI (stable, powerpc64le-unknown-linux-gnu)
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• CI (stable, x86_64-apple-darwin)
• CI (stable, x86_64-unknown-linux-gnu)
• CI (stable, x86_64-unknown-linux-musl)