Router: full support for Dynamic paths (Fix #25)

the router object is now able to handle dynamic Routes that works
with fixed keys and variables, e.g:

  router->map("/user/:id/edit", cb_user_edit);
  router->map("/user/:id/update", cb_user_update);
  router->map("/user/:id", cb_user);

So the following URLS will be available:

  http://host:port/user/28/edit
  http://host:port/user/28/update
  http://host:port/user/28

Signed-off-by: Eduardo Silva <eduardo@monkey.io>