DevGuide lifecycle-hooks issues

[chalin]

• mismatch between Spy Directive video and TS / Dart app behavior: there is no Spy fixing example syntax #4 onInit generated. It goes directly to ng-conf video link #5.

• I don't understand the following statement in the prose; consider revising:

  We also see that the ngOnChanges method is called in contradiction of the incorrect API documentation.

• Counter spy is not fully explained in the prose (maybe it is an exercise for the reader to study it?).

• See DevGuide lifecycle-hooks Peek-A-Boo screenshot inconsistent with app output #1286.

[Drumarcco]

There's also an issue angular/angular#10221 about the documentation stating some hooks are only available to components, when in reality they're also available to directives.

Working on it, I'll make a PR soon.