IE7 support

[Rodrigo Rosenfeld Rosas]

I've changed my IE7 fixes pull request because they weren't enough for handling radio inputs.

Could you please review my last pull request with a partial fix for IE7?

It can't be a complete fix unless we add the parentNode parameter to Serenade.render and append the created node ourselves to the parentNode.

Let me know if you want to take this approach and I can update my pull request:

https://github.com/elabs/serenade.js/pull/53/files

[Rodrigo Rosenfeld Rosas]

I've just published an updated patch.