hakurei 0.2.2

Fixes:
- Handle goexit events more gracefully in `container/stub`.
- Mount `/dev/shm` early to avoid covering mount points from `hst`.
- Compensate parent WaitDelay value for shim timeout.
- Check for nil dbus configuration in `hakurei run`.

Enhancements:
- Initialise `exec.Cmd` early to expose additional methods.
- Leave `$DISPLAY` intact to work around buggy X clients.
- Wrap errno values returned by the `mount` syscall.
- Return dedicated error types for repeated nonrepeatable ops and ops in an
  invalid state.
- Remove generic error wrapping from `internal/hlog`.
- Significantly improve verbose reporting in `container/init`.
- Move `internal/app` error to `hst`.
- Return `hsurc` userid from `cmd/hsu`.

Internal:
- Use default value of NAME_REGEX from adduser for username check.
- Remove `internal/app` interfaces.
- Do not return from shim start.
- Significant cleanups in `internal/app`.
- Replace `internal/sys` with `container/stub`.
- Full test coverage has been achieved in system setup code.
- Move suspendable writer to `container`, in preparation for `internal/hlog`
  removal in [v0.3.x](https://git.gensokyo.uk/security/hakurei/milestone/2).
- Use explicitly shared path in vm tests.
- Assert certain writable paths in vm tests.
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