Have the option of making the sketchfield resize on other events than window resize
I wanted to have a resizable sketch field but when I resize it (change height and width props of SketchField) the canvas stays the same size. To make it work I had to manually trigger the resize event of window. Like this:

```
    componentDidUpdate: function () {
        var sketch = this.refs.sketch;
        var style = this.props.style;
        if (style.width !== sketch._canvas.clientWidth || style.height !== sketch._canvas.clientHeight) {
            window.dispatchEvent(new Event("resize"));
        }
    },
```
