Added an alternative implementation using a wrapper <span> (instead of absolute positioning, see issue #4)

Hi James,

as discussed earlier (see issue #4) I added a new implementation using an additional `<span>` element to avoid absolute positioning on the page. Unfortunately, I don't have the time right now to really test it with a lot of different clients, but it works in IE9 (which is my primary target platform) and *should* work in most others as well, as the differences to your original `span` implementation are only marginal.

Let me know if it works for you as well!

Cheers,
Joschi