title: vuejs update parent data from child component
body: <p>I'm starting to play with vuejs (2.0).
  I built a simple page with one component in it.
  The page has one Vue instance with data.
  On that page I registered and added the component to html. 
  The component has one <code>input[type=text]</code>. I want that value to reflect on the parent (main Vue instance).</p>
  
  <p>How do I correctly update the component's parent data?
  Passing a bound prop from the parent is not good and throws some warnings to the console. They have something in their doc but it is not working.</p>