Added position feature to allow prepend anchor

"Just because it's you" I've spent this morning some extra time trying to add "something really useful" [sic]

Hope that the ability to prepend the anchor (like Github does with markdown) is useful enough and will help you to dominate the world a little bit more with anchorify.js.

Though, the implementation might not please you since I created two intermediate functions (IMO it explains better what they are doing).

Have fun

Best