Bed XY Skew Measurement Strips

__UPDATED 2016nov12:__
* Fixed Customizer bugs (didn't work before - check history below for other changes)
* Uploaded STLs for various bed sizes and 1.75mm filament, plus a pair for Ultimaker 2.85mm. You can use whichever will fit on your bed, but of course you'll get the best accuracy by using Customizer to generate strips specifically for your bed size and minimal skew range.

This OpenSCAD script generates calibration strips that when printed, allow you to determine level of skew in XY