Routing docs should use idiomatic Observable syntax

[robwormald]

Ref: https://angular.io/docs/ts/latest/tutorial/toh-pt5.html

current example:

ngOnInit(): void {
  this.route.params.forEach((params: Params) => {
    let id = +params['id'];
    this.heroService.getHero(id)
      .then(hero => this.hero = hero);
  });
}

This is rather hard to parse (and not exactly side effect free)

Better syntax would be

this.routeParams.flatMap(params => this.heroService.getHero(params.id))

or

this.routeParams.switchMap(params => this.heroService.getHero(params.id))

which would cancel in flight requests - the current syntax has the possibility of an inflight request arriving after the user navigates away.

Note that .switch/flatMap can accept a Promise or an Observable, so its a good place to show interop.