Toy zipline

Changes made to remixes Thing:

Hook now keeps loads centered under wheels
Hole added to hook for accessories or as a guide for a return line
Bushing mounts on body modified to allow bushings to press in and lock
Wheels now have backstop and clips for bushing
Loops added for pull strings in-line with guide rope for stability


There's a 'hollow' variant for faster printing. It's untested.