Add option 'scroll' to disable scrolling

On longer pages where the control isn't going to be obvious, scrolling past it tends to stop the page scroll and change the value on the control.

I added a quick boolean option `scroll` which defaults to true that is used as a conditional for the calls to bind to the mousewheel. This does have the unfortunate effect of disabling the ability to use the mousewheel on the dial completely.

(Also, hi. First pull-request ever, so I hope I'm doing this somewhat right, and if not, sorry, and feel free to ignore it. :smile: )