0.6.0 release candidate 1

What's new since 0.5.10?

• Full rewrite of git-cinnabar in Rust.
• Push performance is between twice and 10 times faster than 0.5.x, depending on scenarios.
• Based on git 2.38.0.
• git cinnabar fetch now accepts a --tags flag to fetch tags.
• git cinnabar bundle now accepts a -t flag to give a specific bundlespec.
• git cinnabar rollback now accepts a --candidates flag to list the metadata sha1 that can be used as target of the rollback.
• git cinnabar rollback now also accepts a --force flag to allow any commit sha1 as metadata.
• git cinnabar now has a self-update subcommand that upgrades it when a new version is available. The subcommand is only available when building with the self-update feature (enabled on prebuilt versions of git-cinnabar).