Delegate method for non-link text selection

Implemented a new optional delegate method on TTTAttributedLabelDelegate for selecting text without links.  I had a TTTAttributedLabel inside a UIButton and wanted the button to fire when non-link text is tapped.  For some reason the button does not receive the touch event despite the [super touchesEnded:withEvent] call that is issued if no link is selected.  Providing a optional delegate callback for this case seems reasonable.