Command line runner

This is something of a selfish pull request.

At my work, we often use waitress by itself without the likes of Paste acting as the runner as we generally delegate serving static assets and the like to the reverse proxy server sitting in front of the application. For applications like that, we use a simple command line runner specific to waitress, effectively a thin wrapper around waitress.serve. I wrote it as it simplified our deployment story quite a bit.

This pull request adapts that code to integrate with waitress properly. Just so as you know, this code and the original runner were written on my own time, not the company's time, so there are no copyright complications involved in merging it into waitress if you think it's worthwhile.