v0.6.1

• Merge release/0.6.1: RunOptions.filesystem and the descriptor door (ADR-0005 §4b)
• Prepare v0.6.1: version and the consumer's changelog
• Merge remote-tracking branch 'origin/feat/descriptor-door' into release-0.6.1
• Merge remote-tracking branch 'origin/feat/run-filesystem' into release-0.6.1
• Merge commit '3631ed9' into feat/run-filesystem
• Let a descriptor's stat say it is a device, a FIFO or a socket
• Keep an entry's full file type in a stat, devices and FIFOs too
• Choose a run's tree per run: RunOptions.filesystem for runNode
• Let a host's tree own its open file descriptions (ADR-0005 step 1)
• Create no command face in a tree a host supplied