Support for name, version, banner, description and a default value

[milesj]

Loving Vorpal, but one feature I miss is a default view. Something that is rendered when the script is called with no command, like node toolkit.js or just toolkit. As of right now, it outputs nothing and simply exits.

It would be nice if we could do something like the following.

vorpal
  .version('1.2.3')
  .name('Toolkit')
  .description('User interface components built on React.')
  .parse(process.argv);

And when ran, would output the following.

  Toolkit v1.2.3
  User interface components built on React.

  Usage: toolkit <command> [options]

  Commands:

    help [command...]  Provides help for a given command.
    exit               Exits application.
    build [options]    Transpile source files.

  Options:

    --version  Output the current application version.
    --verbose  Log more information.

We can even go crazier by supporting banners that prepend to the top.

vorpal.banner(`
 ______   ______   ______   __       __  __   __   ______
/\__  _\ /\  __ \ /\  __ \ /\ \     /\ \/ /_ /\ \ /\__  _\
\/_/\ \/ \ \ \/\ \\ \ \/\ \\ \ \____\ \  _  \\ \ \\/_/\ \/
   \ \_\  \ \_____\\ \_____\\ \_____\\ \_\ \_\\ \_\  \ \_\
    \/_/   \/_____/ \/_____/ \/_____/ \/_/\/_/ \/_/   \/_/
`);

[milesj]

Will tackle possible default action in another PR.