Customizable & Supportless Tray

Remixed from http://www.thingiverse.com/thing:645114

Simplified Roidzo's code to speed up compiling

Note: according to the [Documentation](http://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Primitive_Solids#polyhedron), if your version of OpenSCAD is lower than 2014.03 replace "faces" with "triangles" in the scad file.

Thingiverse Customizer cannot correctly render the feet probably due to the old OpenSCAD engine being used.