The following events were added:

1. `handlestart` - emitted when the router starts to handle the
router stack.
2. `layer` - emitted when a layer is macthed by the router. It
returns the matched layer.
3. `handleend` - emitted when the router has completed handling
the router stack.

I am sure very sure about the name of the events, feedback are
most welcome.

…rend events