Enable transferral of use element's attributes such as transform etc

[Nimdraug]

Currently the whole use element gets replaced by the polyfill. This can cause unexpected issues for polyfilled browsers when attributes other than xlink:href have been applied to the use element.
In my case I had a transform attribute which rotated an icon on my use element and the icon came up unrotated on IE.

So, it would be nice if any extra attributes got copied over (to a g element perhaps) by default or via an option.
Another idea would be to allow there to be a post-processing callback defined in the options.

[shawnbot]

I had exactly this need recently, and I think it should be pretty simple to implement.

[bluemoehre]

I need need this too. Simple X/Y coords at the xlink are ignored.

[bluemoehre]

I added some simple logic in a hurry. See #122
Hope it will be useful or a base for more improvements.

[proimage]

Ditto... need to preserve the X/Y coordinates on the <use> element.