I still do not like that this assumes the label margins are always for portrait labels. I can understand the need to reach into Prawn's initializer to set additional options, but this feels very specific to a limited use case. Let's back out the margin flipping code and merge this in with just the document option for now.

To consider merging in the margin rotation I'd still need to see a few things changed:

1. No line should exceed 80 characters in length (See Line 55)
2. We are already doing too much work in the initialize method. This should be pushed down into it's own method
3. This feature would need to be clearly documented and, ideally, optionally toggled with an additional param

But really I'd prefer if this whole thing is taken care of outside the library. But that doesn't mean I am not open to feedback from you and other developers. If there is a need for this I am willing to hear about it. I'm just trying to avoid feature bloat and strange unexpected behaviors. I would be a little puzzled if setting the `page_layout` to landscape automagically flipped my margins with no way for me to override that.

Thanks @engunneer :cake: