title: Convert one type of list to another RXJava? (Javascript map equivalent)
body: <p>Lets say I have an observable 
  <code>Observable&lt;List&lt;A&gt;&gt;</code> and I want to convert it to an Observable as <code>Observable&lt;List&lt;B&gt;&gt;</code>. Is there any best possible way to convert <code>List&lt;A&gt;</code> into <code>List&lt;B&gt;</code>. Javascript's <code>map</code>'s like implementation would be the ideal situation.</p>