Using Vorpal without `show`

There are a few quirks I've been noticing when using Vorpal without `.show()`.

- without `process.on('SIGINT', () => process.exit(2))`, it doesn't always properly exit and I'm left in some weird limbo where `ctrl-c` will just print `^C`. Even when I kill the process, `ctrl-c` still doesnt do anything but print. its bizarre.

- if you run a command with incorrect parameters, you're left inside the Vorpal shell rather than being dumped back into the commandline

- the delimiter is printed out once at the beginning and once at the end even when you never call `.show()`