Documentation for wat-github

Some sections of the documentation (`@param` lines, `@default` lines, and some of the examples) don't display correctly or at all when I compile the docs, but I just followed the YUIDoc Syntax Reference, and I assume one day `polymer-docs` will be able to handle these lines, so I just left them there.

Also, I added a `files-saved` event to wat-github so that `wat-wat` could set `window.location.hash` rather than `wat-github`, because it makes more sense that way.