docs($routeProvider): document resolveAs and assiging resolve map on scope

[gkalpak]

Related to #13400.

[shahata]

It might be nice to explain that the reasoning behind this feature is to allow passing the resolved locals as bindings to components. Short example:

$routeProvider.when('/', {
  template: '<my-app items="$resolve.items" />',
  resolve: {items: ($http) => $http.get(…)}
});

[gkalpak]

Good suggestion, @shahata. I added another commit with examples with components and other minor improvements. PTAL