Examples break website layout

[`72_InstanceSwappingCanvas.html`](https://github.com/CindyJS/CindyJS/blob/v0.8.0/examples/72_InstanceSwappingCanvas.html) and [`73_InstanceSwappingElt.html`](https://github.com/CindyJS/CindyJS/blob/v0.8.0/examples/73_InstanceSwappingElt.html) break the layout as they append stuff to the HTML body.
