title: labels inside the heatmap rects
body: <p>I would like to display the value of heatMap boxes inside the boxes not just in the tool tip. </p>
  
  <p>Looks although this feature has yet to be added according to: <a href="https://github.com/dc-js/dc.js/issues/1303" rel="noreferrer">https://github.com/dc-js/dc.js/issues/1303</a> , would this be able to be accomplished with d3.js? Thanks.</p>
  
  <p>HeatMap:</p>
  
  <pre><code>        heatMap
              .width(1000)
              .height(400)
              .dimension(dimension)
              .group(filtered_heatMap_group)
              .margins({
                  left: 200,
                  top: 30,
                  right: 10,
                  bottom: 50
              })
              .keyAccessor(function (d) {
                  return d.key[0];
              })
              .valueAccessor(function (d) {
                  return d.key[1];
              })
              .colorAccessor(function (d) {
                  return +d.value.color;
              })
              .title(function (d) {
                  return "Manager:   " + d.key[1] + "\n" +
                      "FTE:  " + d.value.toolTip + "\n" +
                      "Date: " + d.key[0] + "";
              })
              .rowOrdering(d3.descending);
  </code></pre>
  
  <p><a href="https://jsfiddle.net/_M_M_/jvf5ot3p/3/" rel="noreferrer">https://jsfiddle.net/_M_M_/jvf5ot3p/3/</a></p>