Complete support for monitoring extra files for reloading

The [werkzeug-adapted reloader code](https://github.com/falconry/updraft/blob/master/updraft/_reloader.py#L124) has support for adding additional files on which to trigger reload. By default, the reloader looks only for *.py files, but a user may also wish to trigger reload when, say, a configuration file changes.

We would need to plumb through the support for extra files (probably through to the command-line) and add tests.