Node.js compatibility

Node.js compatibility
Add offset and width height to options

Now we can use ean13 at node.js server side node-canvas
`
EAN13=require('../public/js/ean13.js');
(new EAN13()).draw(nodeCanvasInstance, String(number), {
        width:140,
        height:70,
        offsetX:180,
        offsetY:3,
        onSuccess:next
});
`

I use it for a printing on a server side, save to PDF, and send base64 preview to client browser.