title: ReplaySubject replaying value only to the first subscriber
body: <p>Is it possible in RxJava2 to create the <code>ReplaySubject</code> which emits the value only to the first subscriber, which subscribes <strong>after</strong> <code>onNext</code> is called?</p>
  
  <p>Here is the example how is working now:</p>
  
  <pre><code>Subject&lt;String&gt; subject = ReplaySubject.create();
  subject.onNext("hello");
  subject.subscribe(System.out::println); // "hello"
  subject.subscribe(System.out::println); // "hello"
  </code></pre>
  
  <p>And what I want to achieve is the following scenario:</p>
  
  <pre><code>Subject&lt;String&gt; subject = ReplaySubject.create();
  subject.onNext("hello");
  subject.subscribe(System.out::println); // "hello"
  subject.subscribe(System.out::println); // nothing because "hello" have already been emitted
  </code></pre>
  
  <p>I'm assuming, I have to use some transformation between the <code>subject</code> and the <code>subscribe</code> method.</p>