title: Add label to edges in arbor.js (Query plugin)
body: <p>How do I add labels to edges in arbor.js
  It is a graph visualization library.</p>
  
  <p>Suppose A and B are nodes and E is the edge
  One crude way would be insert a "text node" T
  and join A-T and T-B</p>
  
  <p>But i don't want to this, is there any other way?</p>
  
  <p>Here's the sample code</p>
  
  <pre><code>var theUI = {
    nodes:{A:{color:"red", shape:"dot", alpha:1}, 
        B:{color:"#b2b19d", shape:"dot", alpha:1}, 
        C:{color:"#b2b19d", shape:"dot", alpha:1}, 
        D:{color:"#b2b19d", shape:"dot", alpha:1},
    },
    edges:{
        A:{
            B:{length:.8},
            C:{length:.8},
            D:{length:.8}
             }
    }
  }
  
  var sys = arbor.ParticleSystem()
  sys.parameters({stiffness:900, repulsion:2000, gravity:true, dt:0.015})
  sys.renderer = Renderer("#sitemap")
  sys.graft(theUI) 
  </code></pre>
  
  <p>In this, A is connected to B, C and D.
  How to supply label to edges?</p>