Z-frame alignment jig for AM8 printer assembly

Update #2: Uploaded the "V1.1" design which adds some chamfers and rounded corners, so that print artifacts like a squished first layer or overextruded corners don't affect the accuracy of the jig as much.

Update #1: Turned on the customizer feature. Change the "magic_distance" to some other value if you want the jig to be a different length.

The AM8 design requires both Z "towers" to be positioned 127mm from the back of the frame, and holding a ruler while holding everything together and