Bupstash v0.8.0

Another exciting bupstash release for your enjoyment.

Major new features:

• Add bupstash diff command to quickly view a summary of changes between snapshots.
• Remove automatic retry, instead bupstash put attempts to finish all snapshots, even if smeared by concurrent modification.
• Add --allow-list permission that is separate from --get to 'bupstash serve' so you can allow list/list-contents without giving access to snapshot data.
• Speed improvements in many cases for the directory storage backend.

Minor changes and fixes:

• Add blake3 hashes to content index so file contents can be diffed without a full fetch.
• Fix incorrect progress bar accounting.
• Improve smoothness of progress bar.
• Only fetch xattrs on files and directories.
• Support snapshotting device nodes on openbsd.
• Minor improvements to documentation.