#18 Set an aspect ratio for rectangles

[Anonymous]

My ebook reader displays PDFs without the ability to scroll or zoom within a page, thus making the limiting factor for display neither the width or height of a document but the combination of the two. As such, it would be nice to be able to use preset aspect ratios for the rectangles (perhaps with a drop-down of a few sizes such as "Kindle", "Nook", etc) so we can have a more realistic idea of what our end result will be.