Add icons in buttons option

Created by: nolandubeau

First off....Boostrap is awesome!

This is more of a feature request as opposed to an issue. It would great if there were the capability to have an advanced button style that allowed one to add an icon to the left or the right of the button label.

Another cool button feature would be a toggle type button similar to the Twitter "Follow/Un-Follow" button.

Thanks for your great work!

Nolan @nolandubeau