A few important things needs to get this to be 'right':
1a. Have a way to return a response with a status code.
1b. Use that mechanism in the default catchers.
2. Automatically fill in that code from the #[error] handler.
3. Have a way for a responder to say if responding succeeded.
4. Try next highest ranking route if responding with one handler fails.
Here's what works so far:
* The `route` decorator checks its inputs correctly. There's a nice utility
for doing this, and it's working quite well at the moment.
* The `route` decorator emits a `route_fn` and a `route_struct`. The `routes`
* macro prepends the path terminator with the route struct prefix. The
* `Rocket` library can read mount information (though not act on it properly
just yet) and launch a server using Hyper.
