code: function getDepths(depths, callback) {
  
      async.parallel([
          async.apply(store.getStore().getDepth.bind(store.getStore()), depths.parentUrl),
          async.apply(store.getStore().getDepth.bind(store.getStore()), depths.linkUri)
      ],
      function(error, results){
          if (error) {
            return callback(error);
          }
          depths.parentDepth = results[0];
          depths.linkDepth = results[1];
          callback(null, depths);
      });
  }
docs: get the crawl depths for a parent & link uri
  
  
  @param a structure containing both url
  {parentUrl : parentUrl, linkUri : linkUri}
  @param callback(error, depth)