Standalone application launching (linux only; Mac OS partial)

I've merged in my attempt to make a "standalone" webapp.  The idea is that instead of a user interface, your application uses the Chrome Application Shortcut mechanism to launch a Chrome browser window pointing to your application when it launches.  In linux (as long as I haven't broken that side of it by adding the Mac stuff), the application will also try to exit when you close the browser window.  I don't know if you like the idea of this in web.go, but it seems like it might be a logical addition.  If you include it, some future work items would be Windows support (windows supports Chrome's application shortcuts whereas Mac does not), random port numbers and incoming request filtering (to limit/prevent remote access), and I'm sure my code could use some cleanup too.

Oh, and I added a few words about what the handler parameters should be into the source itself, in case I'm not the only one who refers primarily to a local instance of godoc for reference instead of the tutorial site.

Thanks again for this marvelous library!