Expose RouterJS' TypeScript types publicly

The types for public interfaces should be exposed publicly to users who want to consume the types in their application, e.g. EmberJS users.

For example, the Ember Router class method `didTransition` has parameters that are passed in on invocation
https://github.com/tildeio/router.js/blob/73d6a7f5ca6fba3cfff8460245fb5a3ceef8a2b5/lib/router/handler-info.ts#L324

These types are not defined in the Ember JS typings and it's currently not easy to just install and import the router_js types
EDIT: #238 seems like it be related to the issues encountered with importing

Start with lib/router/handler-info.ts at the referenced didTransition parameters, then review issue #238 for the related import problem. Trace how RouterJS declarations are published and imported by consumers. Done means public interface types can be installed and imported by applications such as EmberJS users.

Written by the indexing model from the issue text.