title: d3.js diamond symbol size functionality
body: <p>I want to use "diamond" symbol in D3. 
  I am not sure how the sizing for symbols works in D3. My requirement is:</p>
  
  <pre><code>svg = d3.select("svg"); 
  svg.append("g").append("path")
      .attr("d", d3.svg.symbol()
      .size( function(d) { return 15 })
      .type( function(d) { return "diamond" }))
      .attr("transform", "translate(250, 150)")    
      .style("fill", "black");
  </code></pre>
  
  <p>I want the height of the diamond to be set to 15px. Can anyone help me on this ? Thanks in advance.</p>