publish: Polish/refactor the publishing workflows. * Add a `--preview` option. * The `--list` option gives a nicer output, and prints warnings/errors for incorrect configuration. * Moved most of the `shell` code into a base class that's reusable. * Simplified the code to log publishing to a file. * Nicer output overall, with times.

<ul class="nav navbar-nav navbar-right">
    <li><a href="{{ pcurl('getting-started') }}">Getting Started</a></li>
    <li><a href="{{ pcurl('docs') }}">Documentation</a></li>
    <li><a href="{{ pcurl('api') }}">Code</a></li>
    <li><a href="{{ pcurl('support') }}">Support</a></li>
</ul>