title: q.all for angular2 observables
body: <p>is there something like q.all to resolve all http api requests in angular2?</p>
  
  <p>In angular1, I can do something like this:</p>
  
  <pre><code>var promises = [api.getA(),api.getB()];
  $q.all(promises).then(function(response){
      // response[0]  --&gt; A
      // response[1]  --&gt; B
  })
  </code></pre>
  
  <p>In angular2, the http module returns Observable,</p>
  
  <pre><code>api.getA().subscribe(A =&gt; {A})
  api.getB().subscribe(B =&gt; {B})
  </code></pre>
  
  <p>But I want to resolve A and B together, then do something.</p>