WebApp.run(): Accept host and port args.
WebApp: Add .route() decorator, a-la Flask.
WebApp: Renaming app's attribute to .url_map, for compat with Flask.

It's unclear how much real compatibility this will give, but at least naming
will be consistent.
WebApp.add_url_rule(): Add method for Flask compatibility.

TODO: Arguments don't exactly match, so is this really needed?
test_webapp.py: Use INFO logging by default, DEBUG is too noisy.
Add boldish README.