Tablet holder, saddle surface shape

A tablet computer holder, inspired by the iPad stand [here](http://www.thingiverse.com/thing:443617). This one is optimized for cooking (seeing the recipe), so it has a couple of special features: a rotating tray at the top, to hold a protective film covering your tablet; and another tray at the bottom, holding a cloth for wiping your fingers clean when needed.

In thing files there's also a bit extended version of the 3D-plot SCAD library [here](http://www.thingiverse.com/thing:24897). With the new version you can plot surfaces with given thickness, not only flat-bottom objects with plotted top surface.