[feature] Shell completion

For zsh, the following script can work:

```zsh
#compdef interactively

_arguments -s -S \
  "(- : *)"{-h,--help}"[Show list of command-line options]" \
  "--name[Show list of command-line options]: :{_command_names -e}" \
  '(-)1: :{_command_names -e}' \
  '*:: :_normal'
```

However, it needs #3.
