Adding node and link after render

Is that possible to adding nodes and links to graph after renderGraph function?

How can i do that?

```
var graph = require('ngraph.graph')();
graph.addLink(1, 2);

var renderGraph = require('ngraph.pixel');
var renderer = renderGraph(graph);

//this is not working
graph.addLink(2, 3);
```

The issue names no repository files or tests. Start by reproducing the snippet around renderGraph, renderer, and graph.addLink; done means links added after the initial render are displayed by the renderer.

Written by the indexing model from the issue text.