Attempt to implement the 'disabled' attribute

So after I submitted issue #3 I started playing with the code and came up with this.

It *seems* to work in my app and also in the demo page. But I'm not sure if this is the right approach with x-tag so let me know if there's anything else that needs changing. It's nice that it blends seamlessly with the rest of usual html code and I can do ```switch.disabled = true```, or simply specify ```disabled``` and it works too.