Add routers

[rawleyfowler]

Fixes #37

This PR implements the Router class, that can be used for implementing complex routing schemes.

For example:

use Humming-Bird::Core;

my $router = Router.new(root => '/foo/bar');

# Advice and middleware added will be appended to the routes as they are added.
$router.middleware(-> $request, $response, &next { $response.header('X-MyHeader', 'True') });
$router.advice(-> $response { say $response; $response }); 

$router.get(-> $request, $response { $response.write('abc') }); # Registers a get route on /foo/bar

$route.get('/abc', -> $request, $response { $response.write('abc') }); # Registers a get route on /foo/bar/abc

listen(8080); # No need to register or anything. The router is already registered upon creation.