Add touch support

Hi, I was getting impatient (read: pressure from my project), so I attempted to bring in the work @gregavola had done with touch-support.  Unfortunately, I couldn't make it work, so I started afresh using an approach I've used in other projects before with success.

This time it seems to work well on iDevices.  I don't have Android devices around, but I've heard that this works on them too.

At any rate, it works!  I've also added some simple adjustments to the CSS for touch-devices—namely, made the knob larger so you can actually touch it. =)