title: c3js position of data labels
body: <p>Is there any possible way to change a positions of labels above the data in <code>c3</code> bar chart?
  In official documentation there is well explained how to change positions of labels on x and y measurement axis with manipulation of y and x integer, but I did not found anything for data labels.</p>
  <p>I've tried to point to it with plain <code>d3</code> on which <code>c3</code> is based but <code>console.log</code> returns me null:</p>
  <pre><code>d3.selectAll(&quot;.c3-texts .c3-text&quot;).each(function () {
      var yOrigin = d3.select(this).attr('y');
      console.log(yOrigin);
  })
  </code></pre>
  <p>because it fires before graph generation. You can see and edit what I'm working on here:</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var chart = c3.generate({
    data: {
      columns: [
        ['de', 30],
        ['da', 20],
        ['db', 50],
      ],
      groups: [
        ['de', 'da', 'db']
      ],
      type: 'bar',
      labels: {
        format: {
          y: function(v, id) {
            return id;
          },
        }
      }
    },
    grid: {
      y: {
        lines: [{
          value: 0
        }]
      }
    }
  });
  
  d3.selectAll(".c3-texts .c3-text").each(function() {
    var yOrigin = d3.select(this).attr('y');
    console.log('yOrigin:' + yOrigin);
    //d3.select(this).attr('y',100);
  })</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="http://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"&gt;&lt;/script&gt;
  &lt;script src="http://cdnjs.cloudflare.com/ajax/libs/c3/0.3.0/c3.min.js"&gt;&lt;/script&gt;
  &lt;link href="http://cdnjs.cloudflare.com/ajax/libs/c3/0.3.0/c3.css" rel="stylesheet" /&gt;
  &lt;div id="chart"&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>