Add catch-all routes

[rawleyfowler]

Fixes #30

This allows the user to:

use v6.d;

use Humming-Bird;

get('/foo/**', -> $request, $response { $request.write('Foo **!') });

# Now all requests to /foo/** will hit that end point

# However, you can still define
get('/foo/bar', -> $request, $response { $request.write('Foo Bar!') });

# /foo/bar --> Foo Bar!
# /foo/baz --> Foo **!