title: pluck not found on Rx.observable
body: <p>I'm playing around with <a href="https://github.com/Reactive-Extensions/RxJS" rel="nofollow">https://github.com/Reactive-Extensions/RxJS</a> trying to run through their example using Typescript and Angular 2. When I compile the code it complains that "Property 'pluck' does not exist on type 'Observable&lt;{}>'". I can't figure out why pluck is not available. Did it get removed for rxjs 5?</p>
  
  <p>Using:</p>
  
  <p>angular 2.0.0-beta.0
  rxjs  5.0.0-beta.0</p>
  
  <p>Code:</p>
  
  <pre><code>import {Component} from 'angular2/core';
  import {FORM_DIRECTIVES} from 'angular2/common';
  import {Http} from 'angular2/http';
  import {Observable} from 'rxjs/Observable';
  
  import {Title} from '../providers/title';
  
  @Component({
    selector: 'home',
    directives: [...FORM_DIRECTIVES],
    providers: [Title],
    pipes: [],
    styles: [require('./home.css')],
    template: require('./home.html')
  })
  export class Home {
    wikisearch: any = {};
  
    // TypeScript public modifiers
    constructor(public title: Title, public http: Http) {
      var input = document.getElementById('wikisearch');
  
      /* Only get the value from each key up */
      var keyups = Observable.fromEvent(input, 'keyup')
        .pluck('target', 'value')
        .filter((text) =&gt; text.length &gt; 2);
    }
  }
  </code></pre>