Update Router.js: slashless handleURL, numeric/string params

- Fixes regression where handleURL converted slashless URLs
  to named transitions. Closes #2915
- Numeric/string contexts passed to `linkTo` or
  `transitionTo` convert to params that will be passed
  to the `model`. /cc @ebryn

Closes #2913 (by superseding it)
Merge pull request #2927 from machty/router-js-plus-plus

Update Router.js: slashless handleURL, numeric/string params