Adding text fallback for browsers without canvas (eg. IE8)

This PR allows for browsers that do not support `<canvas>` (*cough* IE8 *cough*) to work. I did not attempt to polyfill canvas or anything like that. Instead, if the browser does not support canvas, a `<div>` is created in place of the `<canvas>` and it's `innerText` is updated when the `Spinner#text()` method is called.

I'll leave this open for a few days for review.