code: function simplify(g) {
    var simplified = new Graph().setGraph(g.graph());
    _.forEach(g.nodes(), function(v) { simplified.setNode(v, g.node(v)); });
    _.forEach(g.edges(), function(e) {
      var simpleLabel = simplified.edge(e.v, e.w) || { weight: 0, minlen: 1 };
      var label = g.edge(e);
      simplified.setEdge(e.v, e.w, {
        weight: simpleLabel.weight + label.weight,
        minlen: Math.max(simpleLabel.minlen, label.minlen)
      });
    });
    return simplified;
  }
docs: /*
  Returns a new graph with only simple edges. Handles aggregation of data
  associated with multi-edges.