Fix boundingBox

In my application I'm scaling image so thresholded image and source image have different sizes. Because of that bounding boxes related to thresholded image could not be applied to source image. I've decided to make ```boundingBox``` in G8RecognizedBlock be normalized *(CGRect with values in 0.0-1.0 range)* and provide additional method to get bounding box for image of target size.

Any suggestions or advices to make it another way?