Multi-windows draft

[pixelpicosean]

It's very easy to create multiple Canvas instances for rendering within browsers, but not possible and useless in a mobile wrapper like Ejecta and CocoonJS. While Mural is designed for desktop this should be a very useful feature.
The proposal lists here:

• Add a "non-standard" renderAsStandalone method to make a canvas as rendering canvas, which will be another window
• Since style property of Canvas does nothing without CSS, it could be used for window and multiple window setups