jKey unbind method

Hi there,
I got a first version of the unbind method implementation. I added a 6th example in samples.html that I'd like you to review so it integrates well with your other ones. So I didn't updated the README file.
I hope you won't be scared of the changes cause there has been a big part of rewriting the way the plugin handles key events bindings. The unbind method was the smallest part.
I'm not convinced it's the better way, nor it's very well optimized, I focused on making it work, so I'm completely open to suggestions about modifications of the way it works or the way if it isn't written the way you did it at first.
Thanks for your review and hope you'll like the patch.