Printrbot Simple Metal Spool holder

Concept leveraged from Emmett's spool holder, but this breaks up the single piece into 3 separate pieces. The problem with the single piece was that it was so long that warping was an issue, leading to many wasted print passes. Individual pieces allows each to be printed separately, then assembled together. The Guide piece, which is the longest piece which tends to warp, was created with a lot of open space beneath, but still strong enough to do its job. I've uploaded a second (improved?) versio