Compact belt tensioner for 20x20 aluminum profiles (Tronxy, Ender...)

This design is suitable for most machines that use belts and 20x20 aluminum extrusions, like the surprisingly good and exceedingly cheap Tronxy X1 printer.

I was inspired by fessyfoos' design and others. However it was redesigned from scratch in Openscad in order to make it significantly smaller, faster and easier to print (e.g. no curved overhang, simpler shapes). Also, this design works as well on X and on Y axis: it will not get in the way of moving bed as it is barely bigger than the foot