iPad Air bracket for 1st/2nd gen BookBook case

A simple bracket to hold the iPad Air (1st gen) in place inside a iPad/iPad2 BookBook case from TwelveSouth (https://www.twelvesouth.com/product/bookbook-for-ipad)

We upgraded from an original iPad to an Air, and these cases are expensive - so instead of buying another, we make it fit!

Thanks to Rich Olson of http://www.nothinglabs.com for PuzzleCut, which allows this to be built on smaller buildplates. It didn't fit on my Replicator2, so I used puzzlecutlib (http://www.thingiverse.com/thi