v0.0.22: Pull hooks, `rm`, more flexible args, better performance

- Cage is now 20× faster!  (It was fairly fast before, now it runs in
  around 0.01 seconds on a fairly large project.)
- We now support pre-`pull` hooks in `config/hooks/pull.d`, so you can
  do things like log into ECR before pulling images.
- The `rm` subcommand can be used to remove stopped containers.
- The `build`, `pull`, `stop` and `up` commands can now take arguments
  of the form `podname`, `podname/servicename` or just `servicename` (if
  unique).